INFLAMMATORY MYOPTHIES

Dr. M. A. SOFIMD; FRCP; (London); FRCPEdin;FRCSEdin

Myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction.

This condition has widely varying etiologies including:

Congenital or inherited, Idiopathic Infectious Metabolic Inflammatory Endocrine Drug-induced or toxic.

Congenital or inherited: Onset in early life with

hypotonia, hyporeflexia, generalized weakness that is more often proximal than distal, and poor muscle bulk

Often with dysmorphic features that may be secondary to the weakness

Relatively nonprogressive

Hereditary Unique morphological

features

INFLMMATORY MYOPATHIES:

Inflammatory Myopahties: Three major diseases identified: Dermatomyositis (DM); Polymyositis (PM); and Inclusion body myositis (IBM).Cause: The cause remains undetermined. All are thought to be due to immune system

abnormalities leading to the development of inflammation in muscle and other tissues

INFLMMATORY MYOPATHIES:

 Dermatomyositis (DM) and polymyositis (PM) are idiopathic inflammatory myopathies, characterized by the shared features of proximal skeletal muscle weakness and by evidence of muscle inflammation.

DM, unlike PM, is associated with a variety of characteristic skin manifestations.

INFLMMATORY MYOPATHIES

A form of DM, termed amyopathic DM, is a condition in which patients have characteristic skin findings of DM without weakness or abnormal muscle enzymes

Epidemiology:  Combined incidence of (DM) and (PM) has

been estimated at 2 per 100,000 annually . Female to male predominance of about two

to one. Peak incidence in adults occurs between the

ages of 40 and 50. Estimates of prevalence range from 5 to 22

per 100,000 .

INFLMMATORY MYOPATHIES

Dermatomyositis (DM) and polymyositis (PM) are both multisystem disorders with a wide variety of clinical manifestations.

Most patients exhibit proximal skeletal muscle weakness.

Several characteristic skin eruptions are typical of DM

Clinical manifestations

Interstitial pulmonary disease, dysphagia, and polyarthritis are also common in DM and PM

Raynaud phenomenon is present in some patients.

Features that overlap with other systemic rheumatic diseases, such as systemic lupus Erythematosus (SLE) and systemic sclerosis (SSc), may also be present.

The risk of malignancy may be increased, particularly in patients with DM.

Clinical manifestations

Muscle weakness: Most common feature

of (DM) (PM). Over 90 percent of

patients with PM present with muscle weakness .

Typically symmetric and proximal in both PM and DM.

Affected muscles include the deltoids and the hip flexors.

Weakness of the neck flexors is also common.

Distal muscle weakness, is mild and does not cause impairment

Cutaneous manifestations often precede or accompany weakness in 50 to 60% of patients with DM.

Mild myalgias and muscle tenderness occur in 25 to 50%.

Clinical manifestations

Skin findings: Several distinct

cutaneous eruptions, which are generally evident at the time of clinical presentation, occur in dermatomyositis (DM) but not in polymyositis (PM)

Characteristics DM:  Gottron’s papules

and the heliotrope eruption are the hallmark and likely pathognomonic features of DM.

Gottron’s sign, photodistributed erythema, poikiloderma, nailfold changes, scalp involvement, calcinosis cutis characteristic and useful in distinguishing DM from PM

Clinical manifestations

Skin findings: Periungual

abnormalities: Capillary nail beds in DM may be erythematous similar to SLE.

Psoriasiform changes in scalp: Scalp resembling psoriasis occur in patients with DM

Calcinosis cutis: Deposition of calcium within the skin, occurs commonly in juvenile DM.

Lung disease: Interstitial lung disease is an important complication in at least 10 percent of cases of DM and PM

Malignancy: An increased rate of malignancy in patients with DM

Esophageal disease: Weakness of the striated muscle of the upper one-third of the esophagus (and/or the oropharyngeal muscles)

Clinical manifestations

Skin findings: Gottron’s sign:

Erythematous to violaceous macules, patches, or papules on the extensor surfaces of joints

Clinical manifestations

Gottron’s sign

Skin findings: Heliotrope

eruption : Erythematous to violaceous eruption on the upper eyelids

Clinical manifestations

Heliotrope eruption

Skin findings: Facial erythema:

Midfacial erythema that can mimic the malar erythema seen in(SLE)

Clinical manifestations

Facial erythema

Clinical manifestations

Holster signGeneralized Erythederma An erythematous and violaceous rash over the

lateral hip, called the "Holster sign,"

Inclusion body myositis (IBM) is the most common age-related muscle disease in the elderly and is an incurable disorder leading to severe disability.

It is a slowly progressive inflammatory myopathy characterised by:

Weakness of the proximal parts of the limbs.

Diminished deep tendon reflexes.

Dysphagia. Mixed myopathic and

neurogenic changes on electromyography

Histologically, features include:

Inflammatory infiltrate. Cytoplasmic

vacuolation. Characteristic tubo-

filamentous inclusions within the cytoplasm and nuclei of muscle cells.

Inclusion body myosisits:

Muscle weakness is the usual presenting feature.

It is painless and insidious, and usually presents after the age of 50.

Weakness is often asymmetrical in contrast to polymyositis.

Fatigue and exercise intolerance are common

Respiratory muscles are usually spared.

Dysphagia is problematic in 40-50% of patients.

Examination Weakness of flexion of

the wrist and fingers is disproportionate compared with any weakness of extension.

Extension of the knee is weak compared with flexion of the hip.

Tendon reflexes are usually suppressed in myopathy and in this condition it is most marked at the knee.

Inclusion body myosisits: Clinical features

Elevated muscle enzyme: CK, LDH, AST, ALT are all muscle enzymes that may be elevated

Autoantibodies, including antinuclear antibodies, in up to 80 percent of patients with DM and PM

Elevated levels of serum and urine myoglobin

The erythrocyte sedimentation rate (ESR) is often normal or is only mildly elevated, even in patients with active muscle disease

Specific autoantibodies: Myositis-specific

autoantibodies are detected primarily in patients with inflammatory myositis and which may offer information regarding prognosis and potential patterns of organ involvement

Myositis-associated autoantibodies are found with other autoimmune rheumatic diseases that may be associated with myositis especially in patients with overlap syndromes

Laboratory findings

ELECTROMYOGRAPHYCharacteristic

electromyography (EMG) are often seen in inflammatory myopathy.

Such changes are not specific for the diagnoses of dermatomyositis or polymyositis,

EMG is normal in 10% of patients.

Similar findings may occur in various infectious, toxic, or metabolic myopathies

MR IMAGING:  Magnetic resonance

(MR) imaging of skeletal muscles is a noninvasive sensitive but nonspecific modality for detecting areas of muscle inflammation and edema with active myositis, fibrosis, and calcification

Laboratory findings

HISTOPATHOLOGY:  Dermatomyositis (DM) and polymyositis

(PM) can be distinguished from each other and from other forms of myopathy by their histopathologic findings.

In patients with dermatomyositis, characteristic findings may also be seen on skin biopsy, although these findings are very similar on light microscopy to changes that can be seen in systemic lupus erythematosus

Laboratory findings

Initial therapy:  The goals of treatment

are to improve muscle strength and to avoid the development of extramuscular complications.

In patients with (DM), resolution of cutaneous disease.

Systemic glucocorticoids:

Initiation with high doses for the first several months to establish disease control

Slow taper to the lowest effective dose for a total duration of therapy between 9 and 12 months

Start with1 mg/kg per day x 6/52

Treatment

Glucocorticoid tapering — After 4-6 weeks tapering should begin.

If no improvement a glucocorticoid-sparing agent should be added

Prednosone should be tapered by 10 mg each week until a dose of 40 mg/day is reached.

After one week on 40 mg/day, the dose should be tapered by 5 mg each week until the 20 mg/day.

After one week on 20 mg/day, the dose should be tapered by 2.5 mg each week until the 10 mg/day

After one week on 10 mg/day dose should be tapered by 1 mg every two weeks until the patient reaches 5 mg/day.

Treatment

Poor prognostic factors include the following:

Advanced age Female sex Interstitial lung disease Presence of anti-Jo-1 (lung

disease) and anti-SRP antibodies (severe muscle disease, cardiac involvement)

Associated malignancy Delayed or inadequate

treatment Dysphagia, dysphonia Cardiac and pulmonary

involvement

Morbidity and mortality:Complications of

polymyositis may include the following:

Interstitial lung disease Aspiration pneumonia Heart block Arrhythmias Congestive heart failure Pericarditis Dysphagia Malabsorption Pneumonia Infection

Myocardial infarction

Morbidity and mortality and prognosis