Motor Neuron Disease
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Direct answer
Amyotrophic lateral sclerosis, the commonest motor neuron disease, is progressive combined upper and lower motor neuron degeneration without sensory, sphincter or ocular involvement (cognitive involvement excepted in the frontotemporal overlap). The Awaji criteria integrate clinical and electrophysiological evidence across bulbar, cervical, thoracic and lumbar regions, treating fasciculations with chronic neurogenic changes as active denervation. Riluzole modestly extends survival, non-invasive ventilation extends it further and improves quality of life, and the rest of care is multidisciplinary and symptom-directed.
What you must remember
- Awaji essentials: upper and lower motor neuron signs progressing within a region suffice with supporting electromyography elsewhere; sensory findings, sphincter disturbance or eye movement abnormality should reopen the differential.
- Electromyography: fibrillations, fasciculations and chronic neurogenic motor unit changes in clinically unaffected muscles widen the territory; nerve conduction remains normal until motor amplitudes fall late.
- Phenotypes: bulbar-onset disease carries the worst prognosis and flail arm a better one; progressive muscular atrophy is lower motor neuron only, primary lateral sclerosis upper motor neuron only and slower, and the ALS-frontotemporal dementia overlap is well defined.
- Genetics: C9orf72 repeat expansion is the commonest familial cause and links ALS with frontotemporal dementia, followed by SOD1, TARDBP and FUS; antisense therapy for SOD1 disease is approved in some countries but negligible in Indian practice, so genetic counselling matters more than genetic promises.
- Disease-modifying therapy: riluzole 50 mg twice daily with hepatic monitoring gives a modest survival gain; edaravone suits selected patients; the phenylbutyrate-taurursodiol combination was withdrawn after its confirmatory trial failed — a lesson in trusting evidence over enthusiasm.
- Respiratory and nutritional care: serial vital capacity with symptom review, non-invasive ventilation improving survival and sleep quality, cough assist for secretions, percutaneous gastrostomy when dysphagia causes weight loss (preferably before advanced respiratory compromise), and sialorrhoea control with anticholinergics or salivary botulinum toxin.
- Mimics to exclude: cervical spondylotic myelopathy with radiculopathy (the classic Indian trap — image the spine), multifocal motor neuropathy with conduction block (treats with immunoglobulin), Kennedy disease (bulbar weakness with gynaecomastia and sensory neuropathy) and post-polio syndromes.
Common confusion
The cervical spine trap deserves respect: spondylotic myelopathy plus radiculopathy reproduces mixed upper and lower motor neuron signs in the arms, and only careful sensory, sphincter and electromyographic assessment separates it from motor neuron disease — a diagnosis never to be made on an unrevised spine MRI. Multifocal motor neuropathy differs by absent upper motor neuron signs, focal conduction block and anti-GM1 antibodies. Bulbar presentations are confused with myasthenia (fatigable, fluctuating) and stroke (sudden). Absence of sensory findings is the motor neuron disease signature; their presence demands a new diagnosis.
Exam-focused takeaway
Learn the four Awaji regions and the rule that fasciculations plus chronic changes equal active denervation. Two treatment answers recur: riluzole 50 mg twice daily and non-invasive ventilation as the survival-and-quality intervention. Expect a mimic stem on cervical spondylosis or multifocal motor neuropathy and a genetics stem on C9orf72 with frontotemporal dementia. Any option promising stem cell cure is wrong.
Frequently asked questions
What are the Awaji criteria?
Progressive upper and lower motor neuron involvement across bulbar, cervical, thoracic and lumbar regions, with electromyographic denervation counting as lower motor neuron evidence.
Which drugs improve survival in ALS?
Riluzole 50 mg twice daily gives a modest benefit, and non-invasive ventilation extends survival further; edaravone suits selected patients.
What is the role of non-invasive ventilation?
It improves survival and quality of life, started for orthopnoea, morning headaches or declining vital capacity.
Which gene is most commonly implicated in familial ALS?
The C9orf72 hexanucleotide repeat expansion, which also links ALS to frontotemporal dementia.
Which treatable mimics must be excluded?
Cervical spondylotic myelopathy with radiculopathy, multifocal motor neuropathy, Kennedy disease and post-polio syndromes.