Motor Neurone Disease: Diagnosis and Management

Introduction

Motor neurone disease (MND) is a progressive neurodegenerative condition causing loss of both upper motor neurones (in the motor cortex and corticospinal tracts) and lower motor neurones (in the brainstem and spinal cord anterior horn), while characteristically sparing sensory pathways, eye movements and sphincter control until very late in the disease, if at all.¹

Amyotrophic lateral sclerosis (ALS) is the commonest and most widely recognised subtype and the term is sometimes used loosely as a synonym for MND, though other patterns exist (see below). MND is relentlessly progressive and currently has no cure, which makes honest, compassionate communication and proactive multidisciplinary care just as central to its management as any specific drug.

It is a favourite exam topic because the clinical pattern - combined upper and lower motor neurone signs with entirely normal sensation - is unique among common neurological diseases and, once recognised, essentially points to the diagnosis on its own.

MND is uncommon, with an incidence of roughly 2 per 100,000 per year and a lifetime risk in the region of 1 in 300. Most cases present between the ages of 50 and 70, with a slight male predominance. Because it is rare and its early symptoms - a dropped foot, a weak grip, slightly slurred speech - are individually unremarkable, the interval from first symptom to diagnosis commonly exceeds a year, and patients are frequently referred first to orthopaedics, ENT or a stroke service before reaching neurology.

Aetiology and subtypes

Most cases are sporadic, with no clear cause identified. Around 5-10% are familial, most often autosomal dominant; the commonest identified genetic causes include mutations in C9orf72, SOD1, TARDBP and FUS. C9orf72 expansions also link MND to frontotemporal dementia, with which it shares pathological (TDP-43) and, in some families, clinical overlap.

Risk factors

• Increasing age (peak onset in the 50s-70s)
• Male sex - a modest excess
• Family history of MND or frontotemporal dementia
• Known genetic mutations (C9orf72, SOD1, TARDBP, FUS) in familial disease
• Smoking - a modestly increased risk in some studies

Clinical features

The presentation reflects a mixture of upper and lower motor neurone dysfunction, and recognising both patterns together, in the absence of sensory loss, is the key diagnostic skill.

Two symptoms that patients rarely volunteer are worth asking about directly. Emotional lability - sudden uncontrollable laughing or crying disproportionate to mood - is distressing and frequently mistaken by families for depression, yet it responds to specific treatment. Sialorrhoea with a weak cough is both socially disabling and a marker of aspiration risk, and identifying it prompts both symptomatic management and a formal swallow assessment.

• Limb-onset disease (the commonest presentation) - asymmetric limb weakness, often first noticed as clumsiness, tripping, or difficulty with fine tasks, with wasting and fasciculations developing alongside upper motor neurone signs in the same or other limbs
• Bulbar-onset disease - dysarthria (slurred or nasal speech) and dysphagia are the first symptoms, with tongue wasting and fasciculation on examination; carries a worse prognosis than limb-onset disease
• Respiratory-onset disease - breathlessness, orthopnoea or recurrent chest infections from early diaphragmatic weakness, an important but easily missed presentation
• No sensory symptoms or signs, no sphincter disturbance, and no oculomotor involvement in typical MND - their presence should prompt reconsideration of the diagnosis
• Emotional lability (pseudobulbar affect) - inappropriate, uncontrollable laughing or crying, from bilateral corticobulbar tract involvement
• Cognitive/behavioural change - a proportion of patients develop frontotemporal dementia, ranging from mild executive dysfunction to a full clinical syndrome
• Weight loss and fatigue

Clinical examination

• Inspection: muscle wasting, fasciculations (best seen with the muscle relaxed and well-lit, classically in the tongue, deltoids, or small muscles of the hand)
• Tone: spasticity in affected limbs
• Power: weakness, often asymmetric, in a pattern that does not fit a single root or peripheral nerve
• Reflexes: paradoxically brisk in a wasted limb - a striking sign that should immediately suggest MND
• Plantar responses: extensor
• Bulbar assessment: tongue wasting and fasciculation, palatal movement, speech quality, cough strength, and a formal swallow assessment
• Sensory examination: should be entirely normal
• Respiratory function: observe for use of accessory muscles, paradoxical abdominal movement, and consider formal spirometry

Differential diagnosis

• Cervical spondylotic myelopathy - can produce combined UMN/LMN signs but usually with neck pain, sensory involvement, and a defined level; MRI cervical spine distinguishes it and should be performed in most suspected MND cases to exclude it
• Multifocal motor neuropathy - a treatable mimic, purely lower motor neurone, with conduction block on nerve conduction studies and anti-GM1 antibodies in some cases; important to exclude since it responds to IVIG
• Inclusion body myositis - progressive weakness, but typically affecting specific muscle groups (finger flexors, quadriceps) with a myopathic rather than neurogenic pattern
• Kennedy's disease (spinobulbar muscular atrophy) - an X-linked LMN-predominant condition with gynaecomastia and a slower course, distinguished genetically
• Myasthenia gravis - fatigable weakness without wasting, fasciculation or UMN signs
• Cervical or lumbar radiculopathy - typically a single root distribution with sensory involvement
• Multiple sclerosis - can cause UMN signs, but with a relapsing course, sensory and visual involvement, and no LMN signs or fasciculations

Investigations

MND remains a clinical diagnosis supported by investigations that both demonstrate the characteristic pattern of denervation and exclude treatable mimics - there is no single confirmatory test.

• Electromyography (EMG) - shows evidence of widespread acute and chronic denervation (fasciculation potentials, fibrillation potentials, and large motor unit potentials) across multiple myotomes/limbs, more extensive than symptoms alone might suggest
• Nerve conduction studies - largely normal (or show only mild changes), which is important in excluding conduction block seen in multifocal motor neuropathy
• MRI brain and spinal cord - primarily to exclude structural mimics, especially cervical myelopathy; may show corticospinal tract changes in MND itself but this is supportive, not diagnostic
• Blood tests - creatine kinase may be mildly elevated; used mainly to exclude alternative diagnoses (thyroid function, B12, anti-GM1 antibodies, and other autoimmune/paraneoplastic markers as clinically indicated)
• Genetic testing - offered where there is a family history, with genetic counselling
• Respiratory function tests - forced vital capacity and other measures, both at diagnosis and serially, to guide the timing of respiratory support

Management

Disease-modifying treatment

Riluzole, a glutamate-release inhibitor, is the principal disease-modifying drug³ and modestly prolongs survival (typically quoted as a few months) without reversing existing deficits or improving symptoms. It is generally well tolerated but requires monitoring of liver function.

Multidisciplinary supportive care

Given the absence of a curative treatment, proactive, multidisciplinary management of symptoms and complications is the mainstay of care and has a substantial impact on both quality of life and survival.

Communicating the diagnosis deserves particular care, and is a frequently examined scenario. It should be done in person, unhurried, with someone the patient chooses present, and with a specialist nurse able to follow up soon afterwards. Patients should not be given a bare prognostic figure without context, since survival varies widely and quoting a median as though it were a personal forecast is both inaccurate and unnecessarily distressing.

It is equally important to avoid the opposite error of therapeutic nihilism. Although no treatment reverses the disease, non-invasive ventilation improves both survival and quality of life, gastrostomy maintains nutrition, and multidisciplinary care demonstrably improves outcomes - so there is a great deal to offer, and saying so explicitly at diagnosis matters.

• Respiratory: regular monitoring of respiratory function; non-invasive ventilation (NIV) is offered once respiratory muscle weakness develops and has been shown to improve both quality of life and survival - one of the few interventions in MND with a clear survival benefit
• Nutrition: dietitian input as swallowing declines; gastrostomy (PEG or RIG) feeding is considered proactively, ideally before severe weight loss or respiratory compromise makes the procedure riskier, to maintain nutrition and reduce aspiration risk
• Speech and language therapy: managing dysarthria and dysphagia, and introducing augmentative and alternative communication (from simple picture boards to eye-gaze technology) before speech is lost entirely
• Physiotherapy and occupational therapy: maintaining mobility and function, equipment and home adaptations, falls prevention
• Symptom control: baclofen or tizanidine for spasticity; standard palliative approaches for excess saliva (drooling), including anticholinergics or botulinum toxin to salivary glands; low-dose opioids and benzodiazepines for breathlessness; treatment of pseudobulbar affect if troublesome
• Psychological support for the patient and family, given the progressive and life-limiting nature of the disease
• Specialist MND multidisciplinary clinic coordinating all of the above, ideally from diagnosis onward

Complications

• Respiratory failure - the leading cause of death, from progressive weakness of the diaphragm and accessory respiratory muscles
• Aspiration pneumonia - from progressive bulbar dysfunction
• Malnutrition and weight loss
• Venous thromboembolism from immobility
• Frontotemporal dementia - in a meaningful proportion of patients, affecting insight, decision-making and family dynamics
• Depression and carer burden - both the patient and family/carers are significantly affected and should be actively supported

Red flags

Most of the urgent decisions in motor neurone disease concern respiratory and nutritional decline, both of which progress predictably and can be anticipated rather than managed reactively. The features below should trigger action before a crisis develops.

Prognosis

MND is relentlessly progressive, and median survival from symptom onset is commonly quoted as around 2-3 years², though this varies considerably: bulbar-onset disease and older age at onset are associated with faster progression and shorter survival, while limb-onset disease and younger age at onset tend to progress more slowly. A minority of patients (including some with primary lateral sclerosis) survive considerably longer. Respiratory failure, often precipitated by an intercurrent chest infection, is the most common cause of death. Early, honest discussion of prognosis alongside proactive multidisciplinary care - rather than either false reassurance or premature nihilism - is central to good management.

Practical planning should begin early rather than at crisis point. This includes discussion of a gastrostomy before weight loss and respiratory decline make the procedure hazardous, introduction of communication aids while speech is still adequate to configure them, and advance care planning covering ventilation and resuscitation preferences. Patients should also be advised about welfare benefits and, in the UK, about eligibility for fast-tracked support, since financial and social pressures compound the burden of the illness considerably.