This document discusses several motor disorders - motor neuron disease, myasthenia gravis, and muscular dystrophy. Motor neuron disease includes ALS and causes progressive weakness and wasting through damage to motor neurons. Myasthenia gravis is an autoimmune disorder causing muscle weakness and fatigability through antibodies blocking acetylcholine receptors. There are several types of muscular dystrophy which are inherited disorders causing progressive muscle weakness and wasting, such as Duchenne muscular dystrophy.

1. Motor disorders
Motor neuron disease
Myasthenia gravis
Muscular dystrophy

2. Motor neuron disease
 Affects motor neurons-
upper-cortical &/or lower-spinal-anterior horn
 Cause- 90% sporadic,
~10% familial- commonest SOD1 mutation
 s/s-
 LMN- progressive weakness, wasting, fasciculation
 UMN- spasticity, exaggerated DTRs, extensor plantar
 Classification-
 ALS- amytropic lateral sclerosis- UMN + LMN
 PLS- primary lateral sclerosis- UMN
 PMA- progressive muscular atrophy-LMN
 Bulbar-LMN & pseudobulbar-UMN palsy

3. Management
 Dx-
 Clinical
 NCV/EMG
 MRI of cervical spine
 Blood tests- TSH, K, Ca, PO4, CPK, VDRL, ANA
 Rx-
 Supportive
 Riluzole- a glutamate inhibitor, for bulbar palsy
 Px-
 Death commonly due to respiratory complications
 ~20% 5 year & ~10% 10 year survival

4. Myasthenia gravis
 An autoimmune disorder, leading to
fluctuating muscle weakness & fatiguability
 Auto-antibodies block acetylcholine receptor
at post-synaptic neuromuscular junction
 s/s- intermittent
 Ptosis, diplopia
 Unstable gait, limb weakness
 Dysphagia, dysarthria, facial muscle weakness
 ~75% have thymus abnormality,
~25% have thymoma

5. Classification
 Class I- ptosis only
 II- + mild weakness of other muscles
IIa- limb/axial
IIb- bulbar/respiratory
 III- + moderate weakness- a/b
 IV- + severe weakness- a/b
 V- requiring mechanical ventilation

6. Diagnosis
 Symptoms +
 Signs of fatiguability of muscles
 Acetylcholine receptor Ab
 EMG- repetitive nerve stimulation test
 IV Edrophonium/Neostigmine test-
temporarily relieve weakness
 CxR/CT scan/MRI- for thymoma
 PFT- spirometry- to assess lung function

7. Treatment
 Drugs-
 Cholinesterase inhibitors- improve muscle function-
Pyridostigmine
 Immunosuppressants- prednisone, cyclosporine,
mycophenolate mofetil, azathioprine
 IVIG/plasmapheresis- in emergency
 Surgery-
Thymectomy, beneficial specially for thymoma

8. Muscular dystrophy
 A group of inherited disorders
 Onset- usually in childhood
 Cause progressive muscle weakness &
wasting leading to falls, difficulty walking,
waddling gait
 Dx- based on specific muscle involvement,
muscle biopsy & raised CPK
 Rx- supportive

9. Types
 Duchenne-
 Commonest
 X-linked recessive; males affected, females carrier
 Due to absence of dystrophin protein
 Onset in childhood
 Causes pseudohypertrophy of calves
 Becker- less severe variant of Duchenne
 Myotonic-
 Commonest in adults, onset- 20-40 years
 Autosomal dominant inheritance
 Affects skeletal, smooth & cardiac muscle
 Facioscapulohumeral
 Limb girdle

10. Types
 Duchenne-
 Commonest
 X-linked recessive; males affected, females carrier
 Due to absence of dystrophin protein
 Onset in childhood
 Causes pseudohypertrophy of calves
 Becker- less severe variant of Duchenne
 Myotonic-
 Commonest in adults, onset- 20-40 years
 Autosomal dominant inheritance
 Affects skeletal, smooth & cardiac muscle
 Facioscapulohumeral
 Limb girdle