A 64-year-old man presents with a eight-month history of generalised weakness


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A 64-year-old man presents with a eight-month history of generalised weakness. On examination he has fasciculation and weakness in both arms with absent reflexes. Examination of the lower limbs reveal increased tone and exaggerated reflexes. Sensation was normal and there were no cerebellar signs. What is the most likely diagnosis?

Progressive muscular atrophy
Amyotrophic lateral sclerosis
Vitamin B12 deficiency
Syringomyelia
Multiple sclerosis

Dr. Kasper:
Amyotrophic lateral sclerosis

‘Fasciculations’ - think motor neuron disease
These symptoms are typical of amyotrophic lateral sclerosis, the most common type of motor neuron disease.

Motor neuron disease: features

Motor neuron disease is a neurological condition of unknown cause which can present with both upper and lower motor neuron signs. It rarely presents before 40 years and various patterns of disease are recognised including amyotrophic lateral sclerosis, progressive muscular atrophy and bulbar palsy

There are a number of clues which point towards a diagnosis of motor neuron disease:

fasciculation
the absence of sensory signs/symptoms*
the mixture of lower motor neurone and upper motor neurone signs
wasting of the small hand muscles/tibialis anterior is common

Other features

doesn’t affect external ocular muscles
no cerebellar signs
abdominal reflexes are usually preserved and sphincter dysfunction if present is a late feature

The diagnosis of motor neuron disease is clinical, but nerve conduction studies will show normal motor conduction and can help exclude a neuropathy. Electromyography shows a reduced number of action potentials with an increased amplitude. MRI is usually performed to exclude the differential diagnosis of cervical cord compression and myelopathy

*vague sensory symptoms may occur early in the disease (e.g. limb pain) but ‘never’ sensory signs