Motor Neuron Disease (MND)

A group of progressive neurodegenerative disorders of unknown aetiology, causing progressive death of motor neurons in the brain, brainstem and spinal cord — usually death within 3–5 years, typically from respiratory failure and dysphagia. The most common form is amyotrophic lateral sclerosis (ALS/Lou Gehrig’s disease). Affects ~9 per 100,000 in Australia; slightly more males than females; mean age of onset ~62, diagnosed ~64 (a ~2-year diagnostic delay is typical). 5–10% of cases are familial (autosomal dominant).

No sensory system or eye-movement (extra-ocular) motor nerve involvement.

Subtypes

• Amyotrophic lateral sclerosis (most common) — combined lower motor neuron atrophy and upper motor neuron hyper-reflexia/spasticity.
• Progressive muscular atrophy — wasting, distal first.
• Progressive bulbar palsy — wasted, fasciculating tongue; weakness of chewing and swallowing (bulbar muscles innervated by CN 9–12).

Presentation

Variable combination of upper limb, lower limb or cranial muscle involvement: foot drop, focal weakness, cramps, fasciculations; bulbar symptoms (swallowing difficulty, slurred speech, dysphonia); stumbling/ spastic gait; emotional instability/depression; muscle pain. Also: constipation, cough, drooling, shortness of breath.

The combination of upper motor neuron AND lower motor neuron signs is the key diagnostic feature.

Diagnosis

Clinical — often difficult, and delayed (patients are frequently initially presumed to have an isolated peripheral disorder, e.g. “foot drop” from lumbar compressive disease, or a laryngeal condition, leading to specialist referrals — neurosurgery, ENT — before eventual neurology referral). Repeat assessment over several months is often needed. Neurophysiology testing and MRI help exclude other conditions.

Examination: cranial nerves; speech and mental affect; tone, reflexes, power and coordination at all levels; cerebellar signs (nystagmus, ataxia, dysdiadochokinesia, hypotonia, gait, balance); cognitive function; peripheral sensation at all levels; fasciculations.

Management

Establishing the diagnosis

Discuss the diagnostic uncertainty with the patient/family and acknowledge the anxiety it causes; request non-acute neurology assessment (confirmation can take a year or more). Arrange community services support for symptoms in the meantime — a confirmed diagnosis isn’t a prerequisite. Once confirmed, offer to discuss advance care planning early, since most patients with MND will eventually lose the ability to communicate.

Disease-modifying therapy

No cure. Riluzole 50mg PO BD modestly slows progression (improves survival by 3–6 months) — monitor for adverse effects: check for neutropenia if a febrile illness occurs (stop if neutropenic); arrange a chest X-ray if a dry cough develops or dyspnoea rapidly worsens (interstitial lung disorder). Edaravone is available as a second option (modest benefit, most effective started early); tofersen (a gene-targeted therapy) is available via compassionate access for the SOD1-mutation subset of ALS.

Multidisciplinary/GP-coordinated care

MND multidisciplinary clinics improve survival compared with standard outpatient care — refer early (either directly, or via the diagnosing neurologist). Teams typically include senior nursing, rehabilitation/ palliative care/respiratory/gastroenterology physicians, neurologists, speech pathology, physiotherapy, OT, social work, psychology/psychiatry and dietetics. The Revised ALS Functional Rating Scale is a simple tool used to track function and predict survival.

Key symptom domains to manage (GP-relevant):

• Respiratory dysfunction — early signs are subtle: morning headache and daytime somnolence (from nocturnal hypoventilation/hypoxia/hypercapnia), progressing to exertional then resting dyspnoea. Early respiratory referral is important — early-onset respiratory failure predicts a worse prognosis. Monitor with respiratory function tests/polysomnography. Non-invasive ventilation (BiPAP) helps once respiratory failure develops. Non-pharmacological measures: upright positioning, pacing activities that trigger dyspnoea. Pharmacological: low-dose benzodiazepines, low-dose morphine.
• Bulbar/communication symptoms — dysphonia/hypophonia/aphonia: voice amplification, communication boards, tablet/smartphone apps, eye-gaze technology.
• Nutrition/swallowing — nutritional supplements; timely PEG or RIG tube insertion and transition to enteral feeding before swallowing fails completely.
• Spasticity — muscle relaxants (baclofen, dantrolene sodium — monitor LFTs closely with dantrolene); baclofen 10mg BD may also help cramps.
• Pain — paracetamol, anti-inflammatories, opioids, gabapentin, pregabalin, TCAs, intra-articular steroid injections, TENS; second-line (specialist-monitored): mexiletine, levetiracetam.
• Sialorrhoea, cough — supportive/symptomatic; specialist input as needed.
• Coordination of care — equipment/mobility support, psychological care, driving advice, financial/transport assistance, community palliative care team involvement as disease stage advances (symptom control in established disease, palliative focus in advanced disease).