CASES OF THE MONTH

MERRF AND KEARNS–SAYRE OVERLAP SYNDROME DUE TO THEMITOCHONDRIAL DNA M.3291T>C MUTATIONVALENTINA EMMANUELE, MD,1 DAVID S. SILVERS, MD,2 EVANGELIA SOTIRIOU, MD,1 KURENAI TANJI, MD, PhD,3

SALVATORE DiMAURO, MD,1 and MICHIO HIRANO, MD1

1Department of Neurology, Columbia University Medical Center, 630 West 168th Street, P&S 4-423, New York, New York 10032, USA2Department of Neurology, Hartford Hospital, Hartford, Connecticut, USA3Department of Pathology and Cell Biology, Columbia University Medical Center, New York, New York, USA

Accepted 20 April 2011

ABSTRACT: A 48-year-old man presented with a complexphenotype of myoclonus epilepsy with ragged-red fibers(MERRF) syndrome and Kearns–Sayre syndrome (KSS), whichincluded progressive myoclonus epilepsy, cerebellar ataxia,hearing loss, myopathic weakness, ophthalmoparesis, pigmen-tary retinopathy, bifascicular heart block, and ragged-red fibers.The m.3291T>C mutation in the tRNALeu(UUR) gene was foundwith 92% heteroplasmy in muscle. This mutation has beenreported with MELAS, myopathy, and deafness with cognitiveimpairment. This is the first description with a MERRF/KSSsyndrome.

Muscle Nerve 44: 448–451, 2011

Since the identification of the first pathogenicmutations in human mitochondrial DNA (mtDNA)23 years ago,1,2 hundreds of large-scale mtDNArearrangements and over 200 mtDNA point muta-tions have been described.3 Point mutations ofmtDNA cause a wide spectrum of syndromes, andmost of them are in transfer RNA (tRNA) genes.Although some mtDNA mutations tend to beassociated with specific clinical syndromes, geno-type–phenotype correlations are imprecise. Manyindividuals who harbor a pathogenic mtDNA muta-tion manifest overlapping features of typical mito-chondrial syndromes.

Myoclonus epilepsy with ragged-red fibers(MERRF) is a multisystem disorder characterizedby myoclonic seizures, cerebellar ataxia, mitochon-drial myopathy, and ragged-red fibers (RRF) onmuscle biopsy, but other common signs includedementia, hearing loss, optic atrophy, peripheralneuropathy, and spasticity. About 80% of MERRFcases are caused by the m.8344A>G mutation inthe tRNALys gene.4

In contrast, Kearns–Sayre syndrome (KSS) is amitochondrial disorder characterized by onset

before 20 years of age of progressive external oph-thalmoplegia or pigmentary retinopathy, togetherwith at least one of a triad of cerebellar ataxia,heart block, and elevated cerebrospinal fluid pro-tein. Typically, KSS is due to single, large-scaledeletions of mtDNA and is almost always sporadic.5

Herein we report the second case of an overlapsyndrome with features of MERRF and KSS in whichthere was a point mutation in the tRNALeu(UUR)

gene (m.3291T>C).

CASE REPORT

A 48-year-old man with a history of premature gray-ing of hair beginning at age 20, hearing loss at age32 years, and depression, presented with chief com-plaints of progressive loss of balance and gait insta-bility with leg weakness for 5 years. At 43 years ofage, he noted intermittent gait imbalance and feltunstable while sitting or standing. Neurological ex-amination revealed mild clumsiness of rapid alter-nating movement and fine finger movements on theleft. Brain magnetic resonance imaging showed cere-bral and cerebellar atrophy (Fig. 1A–C). At age 45,he developed myoclonus epilepsy. An electroence-phalogram (EEG) showed atypical, irregular 2.5–3.5-HZ spike and wave complexes. The patient wassuccessfully treated initially with lamotrigine, thenwith levetiracetam.

There was no history of consanguinity. Themother developed myoclonus epilepsy in her 70s.No other family members presented with similarfeatures.

At 48 years of age, neurological examinationshowed normal cognition, mild cerebellar dysarth-ria, atypical pigmentary retinopathy with normaloptic disks (Fig. 1D), and abnormal eye move-ments with right eye amblyopia and exotropia, leftexophoria, mild bilateral limitation of eye adduc-tion, and saccadic pursuits. In addition, he hadmild proximal leg weakness, left greater than right,dysmetric fine finger movements and heel-to-shinmaneuvers, and impaired tandem gait. Sensationand tendon reflexes were normal.

Laboratory tests revealed mildly elevated serumcreatine kinase at 398 U/L (normal <200 U/L)

Abbreviations: COX, cytochrome c oxidase; ECG, electrocardiogram;EEG, electroencephalogram; KSS, Kearns–Sayre syndrome; MELAS, mito-chondrial encephalomyopathy, lactic acidosis, and stroke-like episodes;MERRF, myoclonus epilepsy with ragged-red fibers; MRI, magnetic reso-nance imaging; mtDNA, mitochondrial DNA; PCR, polymerase chain reac-tion; RFLP, restriction fragment length polymorphism; RRF, ragged-redfibers; SDH, succinate dehydrogenase; tRNA, transfer RNA

Correspondence to: M. Hirano; e-mail: mh29@columbia.edu

VC 2011 Wiley Periodicals, Inc.Published online 15 August 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.22149

Key words: Kearns–Sayre syndrome; mitochondrial DNA; myoclonusepilepsy; point mutation; tRNALeu(UUR); ragged-red fibers

448 MERRF/Kearns–Sayre Syndrome MUSCLE & NERVE September 2011

and resting lactate level of 24.1 mg/dl (normal<22 mg/dl), with normal glucose, thyroid functiontests, parathyroid hormone, and liver functionpanel.

An electrocardiogram (ECG) showed left poste-rior fascicular and incomplete right bundle-branchblocks with right atrial enlargement. Other cardiacfunction tests were normal, including 30-day ECGloop recording, transthoracic echocardiogram, car-diac magnetic resonance imaging (MRI), and tilttable test. Nerve conduction studies and electromy-ography did not indicate signs of myopathy orneuropathy.

METHODS

A right quadriceps muscle biopsy was analyzedwith standard histological and histochemical stains.Biochemical analysis of mitochondrial enzymes inmuscle extracts was performed using previouslydescribed techniques.6

DNA was extracted from muscle by standardprocedures. Screening for mtDNA large-scale rear-rangements was performed on muscle DNA bySouthern blot as described elsewhere.7 DNA fromother tissues was not available. All 22 mitochon-drial tRNA genes were amplified using oligonu-cleotide primers. The polymerase chain reaction(PCR) fragments were then analyzed using a cyclesequencing kit (BigDye Terminator v3.1; AppliedBiosystems) with a genetic analyzer (Model 3130xl;Applied Biosystems).

To quantitate the mutation level, a restrictionfragment length polymorphism (RFLP) study wasperformed on DNA extracted from muscle. A 205-basepair (bp) fragment was obtained with the fol-lowing PCR conditions: one cycle of 94�C for5 min; 35 cycles of 94�C for 1 min, 55�C for 1 min,and 72�C for 1 min; and a final extension step of72�C for 7 min. a-32P-dCTP (3000 Ci/mmol) wasadded prior to the last PCR cycle. Wild-typemtDNA was cut into three fragments (96, 77, and32 bp), whereas mutant mtDNA was digested intotwo fragments (173 and 32 bp) by the enzymeTsp509I. The digestion products were separated ina 15% non-denaturing acrylamide gel and analyzedby a phospho-imager (Molecular Analyst; BioRad,Hercules, California) using ImageQuant software(Molecular Dynamics, Sunnyvale, California) toassess the mutation load.

RESULTS

Muscle biopsy demonstrated multiple RRF onmodified Gomori trichrome staining and numer-ous ragged-blue fibers on succinate dehydrogenasereaction (SDH). Biochemical analysis of respiratorychain enzymes was normal (Table 1).

Genetic tests were negative for the commonMERRF mtDNA mutations (m.3243A>G, m.8344A>G,m.8356T>C, m.8363G>A, and m.8296A>G), and nodeletions in mitochondrial DNA were detected bySouthern blot analysis.

Direct sequencing of the 22 mtDNA tRNAgenes revealed a T-to-C transition at nucleotideposition 3291 in the tRNALeu(UUR) gene. PCRRFLP showed 92% mutant genome in muscle.

DISCUSSION

This patient’s clinical manifestations, together withthe presence of elevated resting lactate blood level,cerebral and cerebellar atrophy on brain MRI, par-tial bifascicular cardiac conduction block, RRF on

FIGURE 1. (A, C) Neuroradiological findings. (A, B) Transverse

sections of fluid-attenuated inversion recovery (FLAIR) brain

MRI study sequences showing cortical atrophy. (C) Sagittal sec-

tion of T1-weighted brain MRI study sequence showing cerebel-

lar atrophy. (D) Left fundus image showing pigmentary

retinopathy. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]

Table 1. Mitochondrial respiratory chain enzyme activities inmuscle.

Enzyme (complex) Control

Patient(% of mean

control values)

Cytochrome c oxidase (IV) 2.80 6 0.52 2.61 (93%)Succinate cytochrome c

reductase (II and III)0.70 6 0.23 0.74 (106%)

NADH cytochrome c

reductase (I and III)1.02 6 0.38 0.75 (74%)

NADH dehydrogenase (I) 35.48 6 7.07 29.90 (84%)Succinate dehydrogenase (II) 1.00 6 0.53 1.39 (139%)Citrate synthase 9.88 6 2.55 9.50 (96%)

Activity expressed as micromoles per minute per gram (lmol/min/g).Control data expressed as mean 6 standard deviation (n ¼ 78). NADH,nicotinamide adenine dinucleotide dehydrogenase.

MERRF/Kearns–Sayre Syndrome MUSCLE & NERVE September 2011 449

muscle biopsy, and myoclonus epilepsy in themother, suggested a mitochondrial disease. Specifi-cally, the patient appeared to have an overlap syn-drome with features of both MERRF and KSS.Myoclonus epilepsy (usually manifesting earlierthan in our patient), sensorineural hearing loss,premature graying, and RRF on muscle biopsy arefeatures of the MERRF syndrome. Brain MRI usu-ally shows brain atrophy with or without basal gan-glia calcification.8 In contrast, ophthalmoparesis,pigmentary retinopathy, partial heart block, anddiffuse white-matter MRI alterations are features ofthe KSS syndrome.9,10 Cerebellar ataxia is commonin both conditions.

Direct sequencing of the patient’s muscle DNArevealed a heteroplasmic mtDNA T-to-C transition atnt.3291 in the tRNALeu(UUR) gene. The m.3291T>Cmutation affects an evolutionarily highly conservednucleotide in the T-w-C loop of the tRNALeu(UUR)

cloverleaf.11 In 2004, Hao and colleagues demon-strated that the m.3291T>C mutation impaired mi-tochondrial tRNALeu(UUR) aminoacylation due toinstability of the mutated tRNA structure, whichmight also inhibit aminoacylation of the wild-typetRNA.12 Furthermore, the mutant tRNA showed par-tial deficiency of the normal taurine modification atthe wobble position, which is required for preciseand efficient codon recognition.13

Point mutations in the tRNALeu(UUR) gene havebeen associated with diverse phenotypes, rangingfrom mitochondrial encephalomyopathy, lactic aci-dosis, and stroke-like episodes (MELAS), to iso-lated myopathy, myopathy and cardiomyopathy,chronic progressive external ophthalmoplegia, anddiabetes mellitus with or without deafness.3 In par-ticular, the m.3291T>C mutation was proven to bepathogenic in previous reports.11,14,15 The firstpatient, described by Goto et al. in 1994, was a 7-year-old Japanese boy affected by MELAS.11 Hisskeletal muscle biopsy showed numerous RRF andstrongly succinate dehydrogenase (SDH)-reactivevessels. Biochemical assays revealed no definitedeficiencies of respiratory chain enzymes in mus-cle. The mutation load in this patient was 86% inmuscle, similar to our patient. Six years later, Uzielet al. found the same mutation in a 7-year-old Ital-ian girl who presented with a 1-year history of pro-gressive leg weakness. A muscle biopsy revealed amild myopathy associated with cytochrome oxidase(COX)-negative fibers and RRF.14 Biochemicalassays on muscle homogenate showed severelyreduced activities of complexes I, III, and IV. Thepatient’s muscle contained approximately 87% mu-tant mtDNA. In 2009, a complete mtDNA analysiscarried out in a large cohort of patients with mito-chondrial disorders detected the same mutation in2 additional patients, a 51-year-old with isolated

mild myopathy and a 12-year-old with deafness andcognitive impairment.15 Both muscle biopsiesshowed RRF/COX-negative fibers, and muscle bio-chemistry revealed normal respiratory chain activ-ities in the patient with isolated myopathy anddecreased complex I activity in the patient withdeafness and cognitive impairment. Mutation loadswere not reported.

As described previously, patients harboring them.3291T>C mutation presented with differentphenotypes. Age at onset ranged from childhoodto adulthood. Clinical phenotype varied from iso-lated myopathy to more complex neurological dis-orders that included deafness and cognitiveimpairment, MELAS, and, as we described here,MERRF/KSS overlap syndrome. Muscle biopsyalways showed mitochondrial abnormalities, butCOX-negative fibers were variably present. The bio-chemical consequences of the mutation were alsodifferent. Despite high mutation loads, both ourpatient and the patient with MELAS had virtuallynormal respiratory chain activities,11,14 whereas thepatient with isolated myopathy described by Uzielet al. had markedly reduced activities of complexesI, III, and IV.14

From a clinical point of view, our patient isstrikingly different from the others, as he repre-sents the first example of MERRF/KSS overlap syn-drome associated with the m.3291T>C mutation inthe tRNALeu(UUR) gene. Interestingly, one previousreport described a patient who also had features ofMERRF and KSS but harbored a differentm.3251A>G mutation within the DHU arm of thesame gene.16 However, compared with our patient,that patient’s phenotype had notable differences,as it included endocrinological problems and mi-graine headache, while lacking cerebellar ataxia,depression, and premature graying. Muscle bio-chemistry also differed. Although the patient withthe m.3251A>G mutation had a lower mutationload (53%) than ours, the activities of complexesI, III, and IV were markedly decreased.

In conclusion, the mechanisms by which muta-tions in tRNA affect respiratory chain activities andhow this correlates with the clinical phenotype arestill largely unknown. Our data reinforce the well-established concept that, in mtDNA-related disor-ders, the same genetic abnormality can be associ-ated with a wide spectrum of phenotypes, and theobservation that tRNALeu(UUR) is a hotspot formtDNA mutations.

This study was supported by the National Institutes of Health(NIH HD32062) and by the Marriott Mitochondrial DisordersClinical Research Fund (MMDCRF). M.H. was supported by NIHgrants (R01HD57543, R01HD056103, and RCNS070232) and bytheMuscular Dystrophy Association.

450 MERRF/Kearns–Sayre Syndrome MUSCLE & NERVE September 2011

REFERENCES

1. Holt IJ, Harding AE, Morgan-Hughes JA. Deletions of muscle mito-chondrial DNA in patients with mitochondrial myopathies. Nature1988;331:717–719.

2. Wallace DC, Singh G, Lott MT, Hodge JA, Schurr TG, Lezza AM,et al. Mitochondrial DNA mutation associated with Leber’s heredi-tary optic neuropathy. Science 1988;242:1427–1430.

3. Brandon MC, Lott MT, Nguyen KC, Spolim S, Navathe SB, Baldi P,et al. MITOMAP: a human mitochondrial genome database—2004update. Nucleic Acids Res 2005;33:D611–613.

4. Yoneda M, Tanno Y, Horai S, Ozawa T, Miyatake T, Tsuji S. A com-mon mitochondrial DNA mutation in the t-RNA(Lys) of patientswith myoclonus epilepsy associated with ragged-red fibers. BiochemInt 1990;21:789–796.

5. Harding AE, Hammans SR. Deletions of the mitochondrial genome.J Inherit Metab Dis 1992;15:480–486.

6. DiMauro S, Servidei S, Zeviani M, DiRocco M, DeVivo DC, DiDonatoS, et al. Cytochrome c oxidase deficiency in Leigh syndrome. AnnNeurol 1987;22:498–506.

7. Naini A, Shanske S. Detection of mutations in mtDNA. Methods CellBiol 2007;80:437–463.

8. Pulkes T, Hanna MG. Human mitochondrial DNA diseases. AdvDrug Deliv Rev 2001;49:27–43.

9. Anan R, Nakagawa M, Miyata M, Higuchi I, Nakao S, Suehara M,et al. Cardiac involvement in mitochondrial diseases. A study on 17patients with documented mitochondrial DNA defects. Circulation1995;91:955–961.

10. Zeviani M, Moraes CT, DiMauro S, Nakase H, Bonilla E, Schon EA,et al. Deletions of mitochondrial DNA in Kearns–Sayre syndrome.Neurology 1988;38:1339–1346.

11. Goto YI, Tsugane K, Tanabe Y, Nonaka I, Horai S. A new pointmutation at nucleotide pair-3291 of the mitochondrial transfer-RNA-Leu(Uur) gene in a patient with mitochondrial myopathy, encephal-opathy, lactic-acidosis, and stroke-like episodes (MELAS). BiochemBiophys Res Commun 1994;202:1624–1630.

12. Hao R, Yao YN, Zheng YG, Xu MG, Wang ED. Reduction of mito-chondrial tRNALeu(UUR) aminoacylation by some MELAS-associ-ated mutations. FEBS Lett 2004;578:135–139.

13. Kirino Y, Goto Y, Campos Y, Arenas J, Suzuki T. Specific correlationbetween the wobble modification deficiency in mutant tRNAs andthe clinical features of a human mitochondrial disease. Proc NatlAcad Sci USA 2005;102:7127–7132.

14. Uziel G, Carrara F, Granata T, Lamantea E, Mora M, Zeviani M.Neuromuscular syndrome associated with the 3291T!C mutation ofmitochondrial DNA: a second case. Neuromuscul Disord 2000;10:415–418.

15. Valente L, Piga D, Lamantea E, Carrara F, Uziel G, Cudia P,et al. Identification of novel mutations in five patients with mito-chondrial encephalomyopathy. Biochim Biophys Acta 2009;1787:491–501.

16. Nishigaki Y, Tadesse S, Bonilla E, Shungu D, Hersh S, Keats BJ,et al. A novel mitochondrial tRNA(Leu(UUR)) mutation in a patientwith features of MERRF and Kearns–Sayre syndrome. NeuromusculDisord 2003;13:334–340.

OPTIC NEUROPATHY ASSOCIATED WITH CANOMAD: DESCRIPTION OF2 CASESLARA SANVITO, MD, PhD and YUSUF A. RAJABALLY, MD, FRCP

Neuromuscular Clinic, Department of Neurology, University Hospitals of Leicester, Leicester LES 4PW, UK

Accepted 26 April 2011

ABSTRACT: CANOMAD is a chronic ataxic neuropathy asso-ciated with IgM paraproteinemia and reactivity against disialosylgangliosides. Ophthalmoplegia is a typical feature, but opticpathway involvement has not been reported previously. Wedescribe 2 cases of CANOMAD associated with optic neuropa-thy. Severe visual loss was present in 1 case. We postulate thatoptic nerve damage may be related to antibody reactivityagainst gangliosides. Our report broadens the spectrum of cra-nial nerve involvement in this rare entity.

Muscle Nerve 44: 451–455, 2011

CANOMAD is an acronym first used in 1996 todescribe a clinico-immunological entity character-ized by chronic ataxic neuropathy, ophthalmople-gia, M-protein, cold agglutinins, and anti-disialosylantibodies.1 This chronic neuropathy presents withclinical features indicative of involvement of boththe peripheral and cranial nerves.2 The diagnosis ismade on the basis of the clinical picture and IgMparaprotein reactivity toward disialylatedgangliosides containing a NeuNAc(a2-8)Neu-NAc(a2-3)Gal epitope on either the internal or ter-

minal galactose of the main oligosaccharide.2 Thesegangliosides include GD1b, GD2, GD3, GT1a,GT1b, and GQ1b. The clinical presentation is heter-ogeneous, and there is a variable degree of antibodyresponse against disialosyl gangliosides. Somepatients do not display all the clinical and laboratoryfeatures of the classical syndrome as detailed in thelargest series reported so far in the literature.2

CANOMAD shares similarities with MillerFisher syndrome (MFS), which is characterized byacute onset of ophthalmoplegia, ataxia, and are-flexia in association with reactivity against GQ1b.The electrophysiological and pathological charac-terization of these patients includes both demyeli-nating and axonal features. Immunomodulatorytreatment with steroids and intravenous immuno-globulin (IVIg) is usually the first-line approach totreat both the acute relapses and the progressivecourse of this condition. Cranial nerve involvementin CANOMAD is well recognized and is usuallycharacterized by ophthalmoplegia with variabledeficits of cranial nerves III, IV, and VI.2 Patientscan present with bulbar symptoms and facial weak-ness. Cranial nerve V can also be affected with fa-cial paresthesiae. The involvement of cranial nerveII with reduced visual acuity and evidence of opticneuropathy has not, to our knowledge, beenreported previously.

We report 2 cases of CANOMAD with clinicaland electrophysiological evidence of optic pathwayimpairment. In the first case there was progressive

Abbreviations: CANOMAD, chronic ataxic neuropathy ophthalmoplegia,M-protein, cold agglutinins, and anti-disialosyl antibodies; CIDP, chronicinflammatory demyelinating polyradiculoneuropathy; CNS, central nervoussystem; IVIg, intravenous immunoglobulins; IVMP, intravenous methylpred-nisolone; MAG, myelin-associated glycoprotein; MFS, Miller Fisher syn-drome; MRC, Medical Research Council; VER, visual evoked response

Correspondence to: Y.A. Rajabally; e-mail: yusuf.rajabally@uhl-tr.nhs.uk

VC 2011 Wiley Periodicals, Inc.Published online 15 August 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.22157

Key words: anti-disialosyl antibodies; ataxic neuropathy; CANOMAD; IgMparaprotein; optic neuropathy

Optic Neuropathy and CANOMAD MUSCLE & NERVE September 2011 451

reduction of visual acuity that resulted in severevisual loss. In this patient the progressive visualdeficit did not respond to IVIg and worsened aftera course of high-dose intravenous steroids. In thesecond case, we found reduced visual acuity andelectrophysiological evidence of optic neuropathywithout other signs of central nervous system(CNS) demyelination.

CASE 1

A 40-year-old man developed an acute episode ofgait imbalance with inability to stand, loss of sensa-tion, and paresthesias in the extremities. He alsonoticed bilateral ptosis without diplopia. He recov-ered within a few weeks and was able to walk inde-pendently, although he still had a mild degree ofataxia. Eight years after his initial onset of symp-toms he noticed gradual deterioration of his bal-ance and mobility with progressive difficulty walk-ing. He was able to walk with a stick until he was50 years of age and started using a walker after-wards. At age 52 he had a second episode of suba-cute deterioration of mobility over a few weeksassociated with facial paresthesiae. He was unableto walk with a walker. He also noticed gradualdeterioration of visual acuity and bilateral ptosisover a few months. There was no family history ofoptic or peripheral neuropathy.

He was assessed during the second relapse,which occurred when he was 52 years of age. Onexamination he had bilateral optic disk pallor onfundoscopy. Visual acuity was 6/9�2 bilaterally.There was mild ptosis, right lateral rectus paresis,and left-beating nystagmus on lateral gaze. There

was mild proximal and distal weakness [MedicalResearch Council (MRC) grade 4] of hip flexionand ankle dorsiflexion. Sensation was diminishedto pin-prick, and vibration and joint position sensewere lost distally in the lower limbs. The patientwas areflexic and had flexor plantar responses.Coordination was reduced in both upper andlower limbs with dysmetria on finger–nose testing.His gait was ataxic and possible only with bilateralsupport. Ten-meter walking time was 25 secondswith a walker.

Immunological screening tests showed an IgMlambda paraprotein with reactivity to several gan-gliosides: GD1a (IgM >1:12,500); GD1b (IgM>1:12,500, IgG 1:1700); GD3 (IgM >1:12,500, IgG1:500); GQ1b (IgM >1:12,500; IgG 1:1100); GT1b(IgM >1:12,500); globoside (IgM 1:1200; IgG1:300); sulfatide (IgM 1:18,000); and GM3 (IgM1:2300). Antibodies to GM1, GM2, GA1, and mye-lin-associated glycoprotein (MAG) were absent.Cold agglutinins were negative. He had an abnor-mal glucose tolerance test but no evidence of overtdiabetes. Further extensive blood tests for autoim-mune, metabolic, and infectious causes of neurop-athy were negative. Genetic studies for Charcot–Marie–Tooth type 1A (CMT1A), myelin protein 0,and connexin32 mutations were negative. Nerveconduction studies showed a severe sensorimotordemyelinating neuropathy with homogeneous slow-ing. There were no forearm conduction blocks,but possible proximal upper limb and forelegmotor conduction blocks were found (Table 1).Brain magnetic resonance imaging (MRI) showedonly an incidental right middle cerebral artery

Table 1. Electrophysiological findings in 2 patients with CANOMAD and associated optic neuropathy.

Motor studiesDistal

CMAP (mV)Proximal/distalCMAP (%)

DML(ms)

Forearm/forelegMNCV (m/s)

Minimum F-wavelatency (ms)

Right median motor (APB) nerveNormal values >5 �70 <4.0 >48 <30

Case 1 7.3 6.5 (Erb’s point)* 5.75 23.9 51.5Case 2 3.6 72.1 (elbow)* 4.95 35.8 39.65

Right ulnar motor (ADM) nerveNormal values >4 �70 <3.3 >48 <31

Case 1 5.1 22.9 (Erb’s point)* 4.55 28.8 57.95Case 2 2.8 6.4 (above elbow) 5.0 28.6 43.5

Right fibular motor (EDB) nerveNormal values >1.5 �70 <6.5 >44 <55

Case 1 2.3 61.1 (fibular head) 5.9 26.3 82.0Case 2 NP NP NP NP NP

Right tibial motor (AH) nerveNormal values >3 �50 <6.1 >44 <55

Case 1 6.4 25.2 (popliteal fossa) 4.45 23.9 78.0Case 2 0.4 54.9 (popliteal fossa) 12.35 15.6 NP

In sensory studies, right radial, median, and sural sensory action potentials were absent in both patients. CMAP, compound muscle action potential; DML,distal motor latency; MNCV, motor nerve conduction velocity; APB, abductor pollicis brevis; ADM, abductor digiti minimi; EDB, extensor digitorum brevis;AH, abductor hallucis, NP, not performed.*All proximal upper limb CMAPs were considered in comparison with CMAPs evoked by distal wrist stimulation.

452 Optic Neuropathy and CANOMAD MUSCLE & NERVE September 2011

aneurysm. A whole spine MRI was unremarkable.Cerebrospinal fluid was acellular with mildly raisedprotein (0.67 g/L; normal <0.45 g/L). Oligoclonalbands were not tested. Visual evoked responses(VERs) showed bilateral delayed responses (>130ms).

The diagnosis of CANOMAD was made on thebasis of the clinical, electrophysiological, and labo-ratory features. The patient was treated with infu-sions of IVIg with improvement of power in hislower limbs and overall mobility. There was alsoless gait ataxia. Infusions have since been requiredevery 4 weeks.

At age 54 years, he complained of progressiveworsening of visual acuity over the preceding 12months. On examination, visual acuity was 6/60 inthe right eye and he could count only fingers withthe left eye. Fundoscopy showed bilateral opticdisk atrophy. Repeat VERs showed poorly formedand irreproducible waveforms. He was treated witha 5-day course of intravenous methylprednisolone(IVMP) that led to transitory worsening of his vis-ual acuity and gait ataxia. He was then treatedagain with IVIg and had stabilization of vision andrapid improvement of ataxia.

CASE 2

An 83-year-old man presented with acute onset ofgait unsteadiness and inability to walk or standunaided. Over the previous 12 months he hadundergone progressively reduced mobility. Hecomplained of leg weakness and reduced sensationin the feet. His balance was poor, but he was stillable to walk independently before the episode ofacute gait deterioration. There was no family his-tory of optic or peripheral neuropathy.

On examination, fundoscopy showed mild bilat-eral pallor of the optic disks. Visual acuity was 6/9�2 and 6/9�1 on the right and left, respectively.There was mild bilateral ptosis without ophthalmo-plegia. There was both proximal and distal weak-ness in his legs (MRC grade 3). He had distallyreduced sensation to pain, temperature, vibration,and joint position in both legs. Deep tendonreflexes were absent in the legs and reduced inthe arms. His gait was severely ataxic and requiredbilateral support. The Romberg maneuver wasstrongly positive. His past medical history includedhypertension, ischemic heart disease, and macro-cytic anemia that was treated with vitamin B12

supplementation.Immunological screen revealed a small IgM

lambda paraprotein (<1 g/L) detected only onimmunofixation and not on electrophoresis. Therewas IgM reactivity to GQ1b (1:300), GM1 (1:2000),GA1 (1:7000), and globoside (1:1300). There wasIgG reactivity to GQ1b (1:1700), GT1b (1:1000),

and sulfatide (1:4000). Antibodies to GM2, GM3,GD1a, GD1b, GD3, and MAG were absent. Coldagglutinins were negative. Further tests for autoim-mune, metabolic, or infectious causes of neuropa-thy were negative. Nerve conduction studiesshowed a sensorimotor axonal-demyelinating neu-ropathy (Table 1). Brain MRI showed signs ofsmall-vessel ischemic disease, and whole-spine MRIshowed signs of multilevel lumbar canal stenosis,but no cord abnormality. Cerebrospinal fluidshowed slightly raised protein (0.52 g/L), normalglucose, and no white cells. Oligoclonal bandswere not tested. VERs showed bilateral delayedresponses (>130 ms).

The diagnosis of CANOMAD was made on thebasis of clinical, electrophysiological, and labora-tory features. The patient was treated initially withinfusions of IVIg without subsequent functionalneurological benefit. He was then treated withhigh-dose oral steroids (1 mg/kg/day). He hadprogressive improvement in power over a periodof weeks with complete normalization of all MRCscores. His joint position sense recovered fully atthe big toes, and the Romberg maneuver normal-ized. He regained the ability to walk without sup-port. Vision was unaltered.

DISCUSSION

We have described 2 patients with CANOMADassociated with signs of optic pathway impairment.Case 1 had classical features and a relapsing–pro-gressive course. He had clinical and electrophysio-logical evidence of severe and progressive opticneuropathy. The visual deficit in this patient didnot respond to treatment with IVIg and worsenedafter a course of IVMP. Case 2 had a CANOMADphenotype with low-level IgM paraprotein and IgMreactivity to GQ1b, GM1, and GA1. This patienthad predominantly motor weakness despite associ-ated and mainly initial ataxia. The reduction in vis-ual acuity was mild.

We are unaware of other reports of visual path-way involvement in CANOMAD, and this suggestsa broader spectrum of cranial nerve pathologythan has been considered previously in this condi-tion. Optic nerve involvement has been describedin a few cases of both presumed and anti–GQ1b-positive MFS, which shares clinical and immuno-logical similarities with CANOMAD.3–6 In somecases there was evidence of both peripheral andCNS involvement.3,4 Optic neuritis in MFS presentsacutely, and the course is either monophasic,5 orrecurrent.6 Both unilateral6,7 and bilateral3–5

involvement have been reported. Optic neuritishas also been described in Bickerstaff brainstemencephalitis, which presents with features of MFSand encephalitic signs.8

Optic Neuropathy and CANOMAD MUSCLE & NERVE September 2011 453

The association between MFS and optic neu-ropathy has been associated with the relative abun-dance of ganglioside GQ1b in the human opticnerve.9 Other abundant gangliosides in the opticnerve include GD1b, GT1b, GD3, and GM1,whereas GD1a is a relatively minor component. Ofnote, delayed VERs have also been reported inpatients with IgM paraproteinemic neuropathyassociated with reactivity to MAG.10 This abnormal-ity was present in 5 of 6 patients with MAG reactiv-ity and in only 1 of 5 patients with IgM monoclo-nal gammopathy and neuropathy without MAGreactivity. This finding has been related to thepresence of MAG and sulfated glucuronyl glyco-lipids in the optic nerve.11 Abnormalities of theVERs have also been described in chronic inflam-matory demyelinating polyradiculoneuropathy(CIDP), and this is considered to be a sign of CNSinvolvement that may sometimes be present ininflammatory neuropathies.12 In a series of 17patients with CIDP, 8 patients had delayed VERs, 3of whom had evidence of increased T2-weightedsignal on brain MRI images.13 There was poor cor-relation with antibody reactivity, as only 2 patientshad antibodies against GM1, sulfoglucuronosyl lac-tosaminyl paragloboside, and anti-sulfatides. Thissuggested that immunological factors differentfrom antibody responses against gangliosides wereprobably related to the occurrence of optic nerveinvolvement in CIDP. Finally, optic neuritis hasbeen reported in multifocal neuropathy with per-sistent conduction blocks (known as Lewis–Sumnersyndrome) and notably in a few of the originalcases.14,15

Our 2 patients did not have evidence of demye-linating changes on brain and spinal MRI thatwould suggest a diagnosis of multiple sclerosis asso-ciated with CANOMAD that could account for thebilateral optic neuropathy. Unfortunately, however,oligoclonal bands were not tested in either case.Other causes of bilateral optic neuropathy (com-pressive, toxic, metabolic, infective, ischemic, orhereditary) were considered in the differential di-agnosis and were excluded either by investigations(screening for vitamin deficiency, syphilis, autoim-mune, and metabolic causes) negative family his-tory, lack of exposure to toxic compounds, and ab-sence of typical presenting features. Brain MRIexcluded compressive or infiltrative causes,although dedicated imaging of the optic nerveswas not performed in either case. Case 1 had high-titer antibodies against several disialosyl ganglio-sides, including GD1a, GD1b, GD3, GT1b, andGQ1b. The lack of CNS demyelination and thehigh-titer antibody reactivity against disialosyl gan-gliosides would suggest a predominant role of thelatter in accounting for the optic nerve damage in

this case, similar to previous reports in MFS. Incase 2 there was a predominant GM1 reactivity andonly low-titer GQ1b antibody response. GM1 is asabundant as disialosyl gangliosides in the opticnerve, and antibody reactivity against GM1 could,on the other hand, explain the optic neuropathyin case 2.9 Also, and interestingly, the high titer ofantibodies to GM1 in case 2 correlated well withhis severe motor weakness. The latter is unusual inCANOMAD and occurs in only about 1 in 5 cases.2

IgM-type anti-GM1 antibody positivity is, on theother hand, well described and correlates with se-verity in chronic pure motor neuropathies such asmultifocal motor neuropathy.16 Our patients didnot otherwise have any IgM reactivity against MAG,which has also been associated with abnormalVERs.10 The mechanism underlying bilateral opticneuropathy in our 2 cases remains unknown in theabsence of any pathological proof. We hypothesizethat either IgM antibodies crossing a loose blood–brain barrier (as occurs in inflammatory neuropa-thies) or IgG reactivity to gangliosides (that wasalso present in our 2 cases) may be involved inthe pathogenic process underlying the opticneuropathy.

Interestingly, our 2 cases had predominantdemyelinating features, as shown in Table 1. Theelectrophysiological characterization of CANOMADis still unclear and involves both axonal anddemyelinating findings.2 It is not clear whetheroptic neuropathy and/or delayed VERs are presentexclusively in cases with predominant demyelinat-ing features, as has been seen in other casesof demyelinating neuropathy (neuropathy associ-ated with anti-MAG reactivity or Lewis–Sumnersyndrome).

It is noteworthy that the optic neuropathy inour 2 patients displayed a variable degree of severityand progression. Case 1 had a progressive andsevere course leading to significant visual loss. Case2 had only mild involvement, although there maybe further progression in the future. The lack ofresponse to immunomodulatory treatment withIVMP or IVIg in case 1 highlights the therapeuticchallenge of optic neuropathy in CANOMAD. Thedeterioration of visual acuity following IVMP incase 1 was unexpected and suggests poor efficacy ofsteroids, which are the usual treatment choice foroptic neuritis. Case 2 did not show any improve-ment in vision in response to steroids, althoughthere was remarkable improvement in motor andsensory function. It is possible that the earlier treat-ment could have hindered the progression of theoptic neuropathy in this patient. The findings fromour 2 patients suggest that optic nerve involvementneeds to be monitored in CANOMAD, as it canpresent subtly and progress gradually over several

454 Optic Neuropathy and CANOMAD MUSCLE & NERVE September 2011

years. The prevention of severe visual impairment isparticularly important in such patients, whose bal-ance and coordination is usually significantlyimpaired by limb and truncal ataxia, which maypartly be compensated by visual control.

In conclusion, we have described 2 cases ofoptic nerve neuropathy in CANOMAD. Our obser-vations show that the spectrum of cranial nerveinvolvement in CANOMAD is broader than hasbeen considered previously. We postulate thatoptic nerve damage may be related to antibodyreactivity against gangliosides, as previously sug-gested in MFS. The progressive course of the opticneuropathy is in keeping with the chronic courseof CANOMAD in contrast to the acute presenta-tion of MFS. Our 2 patients demonstrated variabili-ty in the degree of visual impairment that mayoccur and in the therapeutic difficulties in treatingthe visual loss. These new cases suggest that it maybe important to monitor visual involvement inpatients diagnosed with CANOMAD, as optic neu-ropathy can lead to severe visual loss and contrib-ute significantly to disability. Currently, it remainsunknown whether CANOMAD with associatedoptic neuropathy represents a subtype of the syn-drome, resulting from particular susceptibility ofoptic nerves to immune attack, and/or whetherthis association only occurs with purely demyelinat-ing cases of the peripheral neuropathy. Reports offurther similar cases, as well as investigation ofcases considered to be visually asymptomatic, mayshed light on this in the future.

The authors thank Dr. P.C. Critchley and Dr. M.C. Lawden,Department of Neurology, University Hospitals of Leicester,Leicester, UK, who contributed to the care and referred thereported patients.

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