Motor Neurone Conditions (add)

Question 1

Myasthenia Gravis refers to

Answer 1

an autoimmune disease due to autoantibodies against nicotinic ACh receptors on the NMJ.

– It is more common in women and associated with thymus hyperplasia/thymoma

Question 2

Myasthenia Gravis

Answer 2

– Use dependent muscle weakness –> this worsens with activity and improves with rest

– Starts with eyes (ptosis + diplopia) –> face –> neck –> trunk (giving proximal muscle weakness)

– Symptoms are exacerbated by drugs like Beta-blockers + Lithium + Gentamicin (contraindicated)

Question 3

Myasthenia Gravis tests

Answer 3

– Tendon reflexes are normal.

– Blood test –> shows anti-AchR antibodies, if -ve look for anti-MUSK (tyrosine kinase) antibodies

– However, CK is normal, showing the disease is not a myositis

– Single fibre EMG –> shows decreasing response to repetitive nerve stimulation

– CT scan –> this is needed to look for a possible thymoma (tumour of thymus gland)

Question 4

Myasthenia Gravis management

Answer 4

– Anticholinesterases (e.g. neostigmine) improves stimulation of muscles

– Immunosuppression – Steroids

– Thymectomy – even without thymoma, improves symptoms

N.B. If left untreated can lead to Myasthenic Crisis, a life-threatening weakness of respiratory muscles

– Here, the most important investigation is spirometry to measure the FVC (restrictive conditions)

-Treated with IV immunoglobulins and plasmapheresis (to remove AChR antibodies from circulation)

Question 5

Motor Neurone Disease is characterized by

Answer 5

This is characterized by loss of motor neurones from the motor cortex and anterior spinal horn cells.

– It affects both upper and lower motor neurons, but does not usually affect sphincters

– Motor neurone disease never affects eye movement, and gives no sensory or cerebellar signs

– There are 4 clinical patterns of MND, but most common = Amyotrophic lateral sclerosis (ALS)

Question 6

Motor Neurone Disease symptoms

Answer 6

Gives a mix of upper and lower motor neuron symptoms

– Lower motor signs –> flaccid paralysis with muscle atrophy, fasciculation + impaired reflexes

– Upper motor signs –> Spasticity, rigidity, hyperreflexia, clonus + a positive Babinski sign

– Classic presentation = > 4 years with stumbling spastic gait, weak grip and shoulder abduction

– Wasting of dorsal hand muscles and tibialis anterior

Question 7

Motor Neurone Disease diagnosis

Answer 7

– Nerve conduction studies show normal motor conduction –> excludes neuropathy

– Do brain/cord MRI to exclude structural cause + lumbar puncture to exclude inflammation

Question 8

Motor Neurone disease management

Answer 8

– Managed by a multidisciplinary team as there is no cure available

– Riluzole –> NMDA antagonist is used which improves survival