Motor Neuron Disease — Written Clinical Reasoning

SAQ 1 — Integrated Management of Bulbar-Onset ALS with Respiratory Failure (15 marks, 20 minutes)

Prompt: Outline your integrated management of this patient, addressing the diagnosis, respiratory support, nutritional support, symptom management, multidisciplinary care and advance care planning. Justify each step with reference to physiological thresholds and guideline recommendations. ^[1]

Case vignette: A 66-year-old woman with clinically definite bulbar-onset ALS on riluzole presents with orthopnoea, morning headaches and daytime sleepiness. SNIP 36 cmH2O, supine FVC 35% predicted, pCO2 48 mmHg, bicarbonate 28 mmol/L. BMI 19 with 10 kg weight loss and dysphagia. ^[1]

Model Answer

Confirm the diagnosis and its certainty (2 marks): ^[1]

This patient has clinically definite amyotrophic lateral sclerosis (ALS) by the revised El Escorial criteria — combined upper motor neuron (UMN) and lower motor neuron (LMN) signs in bulbar, cervical and lumbar regions (tongue wasting and fasciculation with a brisk jaw jerk; wasted right arm with brisk reflexes; spastic hyperreflexic legs with extensor plantar responses), with sensation spared ^[4]. The diagnosis should be confirmed by EMG demonstrating active denervation and chronic reinnervation in at least two body regions, MRI of the cervical spine to exclude cervical myelopathy, and a blood screen (including vitamin B12 and creatine kinase) to exclude mimics. Anti-GM1 antibodies and motor nerve conduction studies are warranted if any doubt about multifocal motor neuropathy exists, though the bulbar and UMN signs here make ALS far more likely.

Respiratory support — non-invasive ventilation (4 marks): ^[1]

This patient has symptomatic respiratory muscle weakness crossing guideline thresholds for offering non-invasive ventilation (NIV) ^[1][3]. Specifically: she has symptoms (orthopnoea, morning headache from nocturnal hypoventilation); her sniff nasal inspiratory pressure is 36 cmH2O (below the 40 cmH2O threshold); her supine forced vital capacity is 35 per cent predicted (below 50 per cent); and she has established daytime hypercapnia (pCO2 48 mmHg) with a compensatory respiratory acidosis-buffering bicarbonate of 28 mmol/L. The hypercapnia is a late, ominous sign — she is on the cusp of decompensation.

NIV is the single intervention with the largest survival benefit in ALS, extending median survival by 7 to 13 months in the Bourke randomised trial, with parallel improvement in sleep quality, daytime symptoms and quality of life ^[1]. She should be commenced on bilevel positive airway pressure (BiPAP), titrated to symptoms and nocturnal oxygenation/capnography, beginning overnight and extending to daytime use as the disease progresses. Patient and family education on mask fitting and anticipatory troubleshooting is essential, because tolerance and carer capacity — not physiology — usually determine NIV success. She must NOT be allowed to decompensate further before NIV is established.

Nutritional support — PEG timing (3 marks): ^[1]

She has bulbar disease, dysphagia and significant weight loss (BMI 19, 10 kg lost), all of which independently shorten survival and indicate percutaneous endoscopic gastrostomy (PEG) ^[3]. The critical principle is timing: PEG is safest and most effective before respiratory function falls below an FVC of 50 per cent predicted. Her erect FVC is 52 per cent but her supine FVC is already 35 per cent and she is hypercapnic, so the procedural risk of sedation is now substantial. PEG should therefore be performed urgently, coordinated with the respiratory team for periprocedural NIV, and a radiologically inserted gastrostomy (RIG) should be considered as the safer alternative given her respiratory compromise. The principle is that PEG timing is determined by respiratory surveillance, not by appetite.

Symptom management (2 marks): ^[1]

• Sialorrhoea (likely from impaired swallowing of saliva): hyoscine hydrobromide 1 mg patch every 72 hours, or glycopyrrolate; botulinum toxin into the salivary glands if refractory.
• Spasticity: baclofen, titrated from 5 mg three times daily.
• Pseudobulbar affect: screen for it; treat with dextromethorphan-quinidine (check QT interval first) or an SSRI if contraindicated.
• Pain, constipation, dysarthria (speech therapy and augmentative communication): address proactively. ^[1]

Multidisciplinary care and advance care planning (4 marks): ^[1]

Refer to a specialist multidisciplinary ALS clinic, which independently prolongs survival ^[5]. The team — neurologist, respiratory physician, speech and language therapist, dietitian, occupational therapist, physiotherapist, specialist nurse, palliative care and clinical psychology — coordinates the interventions above.

Because she already has respiratory failure, advance care planning must begin now, while she retains capacity. Cover: goals and fears; the disease trajectory; advance directive and substitute decision-maker appointment; the role and limits of NIV, PEG and tracheostomy ventilation; and the transition to palliative care. Palliative care involvement from diagnosis is increasingly standard. The principle is that withholding unwanted life-prolonging treatment is good palliative care, not euthanasia. Screen for cognitive impairment (ECAS) because frontotemporal dementia coexists with ALS in 15 per cent and predicts poor NIV adherence and shorter survival. ^[1]