Neuromuscular diseases

Dr. Adnan Hamawandi

Definition

Neuromuscular diseases defines disorders of the motor unit characterized by weak muscles and excludes influence on muscle function from the brain, as in spasticity.

The motor unit have four components: 1. The motor neuron in the brain stem or the

anterior horn of the spinal cord. 2. The peripheral nerve. 3. The neuromuscular junction. 4. All muscle fibers innervated by a single motor

neuron.

Spinal muscle atrophies

Are degenerative diseases of the motor neuron that begins in fetal life and continued to be progressive in infancy and childhood.

Werdnig -Hoffmann is the sever infantile form caused by a continuation of programmed cell death that was normal in embryonic life.

The cardinal features are sever hypotonia, generalized weakness, thin muscle mass, absent tendon reflexes, involvement of the tongue, face and jaw muscles while sparing extraoccular muscles and sphincters.

Cont. Werdnig - Hoffmann

Infants soon develop respiratory distress and are unable to feed. They lie flaccid with little movement, unable to overcome gravity, and they lack head control. The heart is not involved and intelligence is normal.

More than 2/3 die by 2 years of age and many die early in infancy.

Serum creatinine phosphokinase is normal, motor nerve conduction studies are normal, and EMG shows fibrillation potentials.

Therapy is supportive.

Guillian –Barrè syndrome

Is a postinfectious polyneuropathy that cause demylination in mainly motor nerves. Lymphocyte sensitized to the basic protein of myelin have been identified in this disease which support the presumed autoimmune pathogenesis.

Typically 2 weeks after a viral infection or immunization, weakness insidiously begins to involve the distal muscles of the lower extremities and progressively involves the trunk, the upper limbs and finally the bulbar muscles. Proximal and distal muscles are involved relatively symmetrically.

Cont. Guillian -Barrè

The onset is gradual and progresses over days or weeks. In cases with abrupt onset tenderness on palpation and pain in muscles is common in the initial stages. Affected children are irritable and bulbar involvement occur in about half of cases. Respiratory insufficiency may result . Urinary incontinence or retention is usually transient. Tendon reflexes lost. The clinical course is usually benign and spontaneous recovery begins within 2-3 weeks. Most patients regain full strength although few are left with residual weakness.

Cont. Guillian -Barrè

CSF studies are essential for diagnosis. The CSF protein is elevated to more than twice the upper limit of normal, glucose level is normal while there is no pleocytosis. Fewer than 10 cells are found.

Motor nerve conduction velocities are greatly reduced and EMG shows evidence of acute denervation of muscle.

Treatment

Patients in early stages should be admitted and observed for respiratory muscle involvement which may need mechanical ventilation.

Rapidly progressive paralysis is treated with IV Immunoglobulin. If ineffective Plasmapharesis, Steroids, and Immunosuppressive drugs are alternatives.

Patients with slow progression may simply be observed for stabilization and spontaneous remission without treatment.

Supportive care is important.

Duchenne muscular dystrophy

An X-linked recessive inherited disease with abnormal gene on Xp21 locus encoding for cytoskeletal protein known as Dystrophin that is present in brain, skeletal muscle, and cardiac muscles.

Symptoms typically begin at 2-4 years of age. Independent walking may be delayed, affected children never run normally and never walk upstairs using alternating feet. An early Gower sign is often evident by 3 years of age, and is fully expressed by 5-6 years, waddling gait appear at this time.

Cont. Duchenne

Cardiomyopathy is a constant feature of this disease. The severity of cardiac involvement

does not necessarily correlate with the degree of skeletal muscle weakness.

Enlargement of the calf muscles and wasting of thigh muscles is a classic feature.

Intellectual impairment occur in all patients although only 20-30% have an IQ less than 70.

The patients are wheelchair bound by 12 years and die between 18-25 years of age usually from respiratory failure, heart failure, or pneumonia.

Cont. Duchenne

Serum creatinine phosphokinase is greatly elevated,10-20 times the normal( normal value <160U/L). EMG is consistent with myopathy but non specific. A specific molecular diagnosis is possible by demonstrating deficient or defective dystrophin by immunohistochemical staining of sections of muscle biopsy OR by DNA analysis from peripheral blood.

Therapy is supportive.