Motor Neuron Disease — Viva Defence

Viva Part 1 — Long-Case Defence (Bulbar-Onset ALS with Respiratory Failure)

Candidate's opening statement (SASPOP)

"This is Mrs R, a 66-year-old retired librarian presenting with a 14-month history of progressive dysarthria and dysphagia, a 6-month history of right-hand weakness, and a 2-month history of orthopnoea and morning headache, with 10 kilograms of weight loss. Her principal problems are clinically definite bulbar-onset amyotrophic lateral sclerosis with established respiratory muscle weakness, nutritional decline requiring urgent PEG, and the need to begin advance care planning while she retains capacity." [1]

Examiner: "Present your problem list and integrated management plan."

Problem 1 — Clinically definite ALS (bulbar onset). Combined UMN and LMN signs in bulbar (wasted fasciculating tongue, brisk jaw jerk), cervical (wasted right hand with brisk reflexes) and lumbar (spastic hyperreflexic legs, extensor plantar) regions, with sensation spared — meeting revised El Escorial criteria for clinically definite ALS [5][4]. Confirm with EMG (widespread denervation and reinnervation), MRI cervical spine to exclude cervical myelopathy, and a blood screen including B12. She is already on riluzole 50 mg twice daily — correct — and I would monitor liver function and full blood count [2].

Problem 2 — Symptomatic respiratory muscle weakness. She has orthopnoea and morning headache; her sniff nasal inspiratory pressure is 36 cmH2O (below 40), supine FVC 35 per cent predicted (below 50), and she is hypercapnic (pCO2 48 mmHg). She meets guideline criteria to be offered non-invasive ventilation — the single intervention with the largest survival benefit (median 7 to 13 months) [1][3]. I would initiate BiPAP, titrated to symptoms and nocturnal capnography, and educate the patient and family on mask management. I would not wait for worsening hypercapnia.

Problem 3 — Nutritional decline and dysphagia. BMI 19, 10 kg weight loss, dysphagia. PEG is indicated — but because her respiratory function has already fallen below the 50 per cent predicted FVC safety threshold, I would coordinate periprocedural NIV and consider a radiologically inserted gastrostomy (RIG), which is safer in respiratory compromise [3]. The principle is that PEG timing is set by respiratory surveillance, not by appetite.

Problem 4 — Symptom control. Hyoscine patch for sialorrhoea; baclofen for spasticity; dextromethorphan-quinidine for pseudobulbar affect (after an ECG); speech therapy and augmentative communication for dysarthria. [1]

Problem 5 — Multidisciplinary care and advance care planning. Specialist MND clinic referral (independently prolongs survival); begin advance care planning now while capacity is intact — goals, advance directive, substitute decision-maker, the future role of tracheostomy ventilation, and palliative care involvement from diagnosis [3]. Screen for cognitive impairment with the ECAS, because ALS-FTD coexists in 15 per cent and predicts poor NIV adherence.

Probing questions

Examiner: "Why is NIV the most important intervention here, and what determines its success?" "Because respiratory failure is the usual cause of death in ALS, and NIV is the only intervention with a survival benefit measured in months rather than weeks — a median of 7 to 13 months in the Bourke randomised trial, with quality-of-life gains [1]. Success is determined less by physiology than by tolerance and carer capacity: poor mask fit, secretion overload, claustrophobia and carer exhaustion are the commonest reasons NIV fails. So I would invest in mask fitting, humidification, secretion management, and family education, and I would screen for cognitive impairment that would impair adherence."

Examiner: "What is your threshold for starting NIV, and why not wait for hypercapnia?" "My threshold is symptoms plus objective weakness: a sniff nasal inspiratory pressure below 40 cmH2O, or an FVC below 50 per cent predicted, or a supine-erect FVC drop of more than 25 per cent [3]. Daytime hypercapnia is a LATE sign — by the time the pCO2 is high, the patient is on the verge of decompensation and may need emergency intubation or a comfort-care pathway. The point of surveillance every three months is to intervene before that point."

Examiner: "She asks whether riluzole is worth taking. What do you say?" "I tell her honestly that riluzole is the best-established disease-modifying drug, that it extends median survival by about three months in pooled trial data, that it is not a cure and does not arrest the disease, and that it is generally well tolerated with monitoring of liver function and blood count [2]. I frame the modest benefit alongside the larger gains from NIV and multidisciplinary care, so she understands riluzole is one part of a package, not the whole answer."

Examiner: "How do you begin the advance care planning conversation?" "I start early, while she retains capacity, and I return to it at intervals. I ask what matters most to her, what she fears, and what she would and would not want if she could not speak for herself. I explain the likely trajectory and the future decisions (escalation of NIV, tracheostomy ventilation, PEG, end-of-life symptom control). I help her appoint a substitute decision-maker and document an advance directive. I emphasise that choosing to limit unwanted treatment is good palliative care, and I involve palliative care from diagnosis." [1]

Viva Part 2 — Short-Case Discussion (Combined UMN and LMN Signs)

Examiner: "Take me through your examination of a patient you suspect has motor neuron disease."

"I inspect first — looking for wasting (thenar eminence, first dorsal interosseous, intrinsic foot muscles, quadriceps, and the tongue at rest in the floor of the mouth, never protruded, because protrusion induces normal fasciculations). I look for fasciculations in the forearm, thigh and tongue. I assess tone in the arms and legs, looking for the velocity-dependent catch of spasticity. I test power group by group, proximal and distal, comparing sides, and record an MRC grade. I check the reflexes — biceps, triceps, supinator, finger jerks, knee and ankle jerks, and the plantar responses — and I look specifically for the paradox of a wasted, weak muscle with a preserved or brisk reflex, which is highly suggestive of ALS. I test coordination, knowing that spasticity slows rapid alternating movements rather than cerebellar ataxia. I test all sensory modalities to confirm they are spared. I examine the cranial nerves and bulbar muscles — tongue bulk and movement, palate, jaw jerk, gag — and assess speech. Finally, I watch the patient walk." [1]

Examiner: "What signs would confirm the diagnosis?"

"The diagnostic signature is combined UMN and LMN signs in the same body regions, with sensation spared. So I would look for: a wasted, fasciculating tongue with a brisk jaw jerk (bulbar region); wasted, fasciculating hand muscles with brisk finger jerks (cervical region); and spastic, hyperreflexic legs with extensor plantar responses (lumbar region). The coexistence of a wasted muscle with a brisk reflex in the same limb is the bedside paradox that defines ALS." [1]

Examiner: "What is your differential, and how do you exclude cervical myelopathy?"

"My differential for combined UMN and LMN signs is cervical myelopathy (the commonest mimic), and for pure LMN signs it is multifocal motor neuropathy, Kennedy disease, B12 deficiency and inclusion body myositis. The discriminator between ALS and cervical myelopathy is the bulbar and rostral involvement: a cervical cord lesion can produce LMN signs in the arms and UMN signs in the legs, but it cannot explain tongue wasting and fasciculation, a brisk jaw jerk, or UMN signs above the level of the lesion. So the presence of bulbar signs clinches ALS, and an MRI of the cervical spine excludes the structural mimic. I would also send motor nerve conduction studies to exclude conduction block (MMN), B12, creatine kinase, and — if indicated — anti-GM1 antibodies and genetic testing [4]."

Examiner: "What would the EMG show?"

"Active denervation — fibrillation potentials and positive sharp waves — together with chronic reinnervation — large, polyphasic motor unit potentials with reduced recruitment — in at least two of the four body regions, with normal sensory studies and no conduction block [4]. Under the Awaji criteria, fasciculation potentials in affected muscles count as equivalent evidence of active denervation. The combination of active and chronic change in the same muscle is the electrophysiological signature, because ALS is both destroying motor neurons (active) and the surviving neurons are reinnervating denervated fibres (chronic) simultaneously."

Examiner: "Name the two most testable exam pitfalls in MND."

"First, attributing combined arm-wasting and leg-spasticity to cervical myelopathy alone when bulbar signs are present — bulbar involvement cannot come from a cervical cord lesion and clinches ALS. Second, confusing multifocal motor neuropathy (MMN) with ALS — MMN has no UMN signs, is asymmetric and upper-limb distal, has conduction block and anti-GM1 antibodies, and responds to IVIG; ALS does not respond to IVIG, and missing MMN denies a patient years of function." [1]