Neurological Examination of the Upper Limbs — Written Clinical Reasoning

SAQ 1 — Upper Limb Neurological Examination: Localisation, Diagnosis, and Differential (20 marks, 30 minutes)

Prompt: Outline your systematic approach to this patient's upper limb neurological examination, addressing: (a) the eight-step examination routine and how each step contributes to the localisation; (b) the interpretation of the combined upper and lower motor neuron signs and the most likely diagnosis; (c) the differential diagnosis and how you would exclude the key mimics; (d) the investigations you would arrange; (e) the cranial nerve and lower limb findings you would specifically seek to complete the assessment; and (f) the common examination trap in this case. [1]

Model Answer

(a) The eight-step examination routine (4 marks): [1]

My systematic routine is inspection, tone, power, reflexes, coordination, sensory, cortical sensory, and functional testing — performed in the same order every time, because each step builds on the last to localise the lesion. [1]

On inspection, I note the wasting of the intrinsic muscles of both hands — the dorsal interossei (the guttering between the metacarpals), the thenar eminence, and the hypothenar — which indicates lower motor neuron involvement of the C8/T1 myotomes and the intrinsic hand muscles. I note the fasciculations in the deltoid, biceps, and first dorsal interossei, which indicate anterior horn cell or motor axon irritability. The combination of wasting and fasciculations across multiple myotomes (C5 deltoid, C5/6 biceps, C8/T1 interossei) indicates widespread LMN involvement. [1]

On tone, the increased spastic tone indicates upper motor neuron (corticospinal tract) involvement. [1]

On power, the weakness in the finger abductors (T1, ulnar nerve), thumb opposition (T1, median nerve), and shoulder abduction (C5, axillary nerve) confirms the widespread LMN pattern, but the preserved bulk and the pyramidal-predominant pattern in some muscles would need to be assessed. [1]

On reflexes, the brisk biceps, supinator, and triceps with a positive Hoffman sign confirm the UMN involvement above the C5/C6 level. [1]

On coordination, the finger-nose test is limited by weakness, which I explicitly note — I do not call this "dysmetria." [1]

On sensory, the intact sensation is a critical negative finding — it argues against a peripheral neuropathy, a radiculopathy, or a spinal cord lesion, all of which would produce sensory loss. [1]

On cortical sensory and functional testing, I would test stereognosis, graphesthesia, and a button task. [1]

(b) Interpretation of the combined UMN and LMN signs (4 marks): [1]

The combination of lower motor neuron signs (wasting, fasciculations, weakness) with upper motor neuron signs (increased spastic tone, brisk reflexes, positive Hoffman sign) in the same patient, with intact sensation, is the clinical signature of motor neuron disease (amyotrophic lateral sclerosis). The El Escorial Revised criteria require the combination of UMN and LMN signs in multiple body regions, with progression over time, and the exclusion of mimics [1]. The Gold Coast criteria simplify this to a dichotomous "ALS or not ALS" classification with a demonstrated sensitivity of 92 per cent [2]. The intact sensation is the critical negative finding — motor neuron disease is a pure motor disorder, and any sensory loss should prompt a search for an alternative diagnosis.

(c) Differential diagnosis and exclusion of mimics (4 marks): [1]

The key mimics of MND that I must exclude are: [1]

• Cervical spondylotic myelopathy — can cause LMN signs at the level of the cord compression and UMN signs below it. The discriminator: cervical myelopathy produces a sensory level or sensory loss in the upper limbs, and the LMN signs are confined to the myotomes at the compressed level. The widespread fasciculations (deltoid, biceps, interossei) across multiple levels, and the intact sensation, argue against cervical myelopathy. I would confirm with an MRI of the cervical spine.
• Multifocal motor neuropathy with conduction block — a pure LMN disorder (no UMN signs) that mimics the progressive weakness and wasting of MND but is treatable (intravenous immunoglobulin). The discriminator: MMN does not cause increased tone or brisk reflexes, and the weakness is in the distribution of individual nerves rather than being widespread. I would confirm with nerve conduction studies showing conduction block.
• Cervical radiculopathy with a coincidental myelopathy — the LMN signs in the arms with UMN signs in the legs. The discriminator: the widespread fasciculations across multiple levels and the UMN signs in the arms themselves (not just the legs) argue against this.
• B12 deficiency (subacute combined degeneration) — causes dorsal column loss and corticospinal tract signs, but not LMN wasting and fasciculations. The intact sensation and the prominent LMN signs argue against this. [1]

(d) Investigations (3 marks): [1]

My investigation plan is: [1]

1. Needle electromyography and nerve conduction studies — the cornerstone. The EMG shows the denervation (fibrillation potentials, positive sharp waves) and reinnervation (large, polyphasic motor unit potentials) in at least two spinal regions (cervical, thoracic, bulbar, lumbosacral) that confirms anterior horn cell disease. The nerve conduction studies exclude a demyelinating neuropathy (normal conduction velocities, no conduction block — excluding MMN and CIDP).
2. MRI of the brain and cervical spine — to exclude a structural mimic (a cervical cord compression, a foramen magnum lesion, a multiple sclerosis plaque).
3. Blood tests — a full blood count, urea and electrolytes, liver function, thyroid function, vitamin B12, creatine kinase, and a serum protein electrophoresis — to exclude metabolic and infectious mimics.
4. Lumbar puncture — if the CSF protein is elevated (above 1 g per L), this raises a paraproteinaemic neuropathy, which is a treatable mimic. [1]

(e) Cranial nerve and lower limb findings (3 marks): [1]

To complete the assessment, I would examine the cranial nerves for bulbar involvement — tongue wasting and fasciculations (the single most specific sign of bulbar-onset MND), a brisk jaw jerk (a UMN sign of pseudobulbar palsy), and a depressed gag reflex. I would examine the lower limbs for the mixed pattern — wasting and fasciculations (LMN) with brisk reflexes, increased tone, and an upgoing plantar response (UMN). I would assess the gait — a spastic or a foot-drop gait may indicate lower limb involvement. I would also assess the respiratory function — the forced vital capacity and the sniff nasal inspiratory pressure, because respiratory muscle weakness is the commonest cause of death in MND and its early detection triggers the discussion of non-invasive ventilation. [1]

(f) The common examination trap (2 marks): [1]

The trap is failing to recognise the mixed UMN and LMN pattern and diagnosing either a pure UMN or a pure LMN disorder. The candidate who sees the wasting and fasciculations and diagnoses a peripheral neuropathy (missing the brisk reflexes and the increased tone) has undercalled the diagnosis. The candidate who sees the increased tone and brisk reflexes and diagnoses a cervical myelopathy (missing the widespread fasciculations and the intact sensation) has missed motor neuron disease. The key teaching point is that the combination of a wasted, fasciculating muscle with a brisk reflex in the same limb is the "ALS reflex" — the pathognomonic sign of the disease — and it should be actively sought and presented. The candidate who presents this combination clearly and offers MND as the diagnosis, with the appropriate investigations to confirm and exclude mimics, has demonstrated the core neurological competency the DCE short-case station is testing [1][2].

SAQ 2 — The Inverted Supinator Sign and Cervical Myelopathy (10 marks)

Prompt: A junior doctor asks you to explain: (a) the inverted supinator sign and its mechanism; (b) the other bedside signs of cervical myelopathy and their diagnostic accuracy; and (c) the synthesis of the evidence (with the systematic review by Rhee and colleagues) that you would give a colleague considering the reliability of physical examination maneuvers for cervical myelopathy. [1]

Model Answer

(a) The inverted supinator sign (3 marks): [1]

The inverted supinator sign is tested by striking the brachioradialis tendon (the radius just above the wrist) and observing the response. In a normal patient, the response is elbow flexion (the C5/C6 reflex arc). In the inverted supinator sign, the expected elbow flexion is absent or diminished, and instead there is paradoxical finger flexion (a C8 response). The mechanism: a lesion at the C5/C6 level in the cervical cord (most commonly cervical spondylotic myelopathy at C5/C6) interrupts the afferent limb of the supinator reflex arc (so the C5/C6 response is lost), and simultaneously interrupts the descending corticospinal tract at that level, removing the inhibitory influence on the reflex arcs below the lesion (so the C8 finger jerk becomes exaggerated). The inverted supinator sign, combined with a brisk triceps reflex and a positive Hoffman sign, is the classic bedside triad of cervical myelopathy at C5/C6. [1]

(b) Other bedside signs and their diagnostic accuracy (4 marks): [1]

The other bedside signs of cervical myelopathy are: [1]

• Hoffman sign — flicking the middle fingernail produces flexion and adduction of the thumb. A systematic review found variable sensitivity (approximately 20 to 60 per cent across studies) for cervical myelopathy [3]. A bilateral or markedly asymmetric Hoffman sign is more clinically significant than a weakly positive unilateral finding, which may be present in up to 3 per cent of healthy individuals.
• Hyperreflexia — brisk reflexes in the upper and lower limbs, with clonus at the ankle or the wrist.
• Upgoing plantar response (Babinski sign) — a UMN sign in the lower limbs.
• Spastic gait — the wide-based, stiff, scissoring gait of bilateral corticospinal tract involvement.
• Lhermitte sign — an electric shock sensation down the spine on neck flexion, indicating posterior column irritation in the cervical cord.
• Sensory level — loss of pinprick below a line on the trunk or the upper limbs.

(c) Synthesis of the evidence (3 marks): [1]

The synthesis I would give the colleague is that the physical examination maneuvers for cervical myelopathy, while useful for screening, have variable and sometimes disappointing diagnostic accuracy [3]. No single physical sign reliably confirms or refutes the diagnosis — the Hoffman sign alone has a sensitivity as low as 20 per cent in some studies, meaning it is frequently absent in early or mild myelopathy. The value of the physical examination is in the combination of signs (the inverted supinator, the Hoffman, the hyperreflexia, the gait, the sensory level) that together raise the pre-test probability and guide the decision to image. The MRI of the cervical spine is the gold standard for diagnosis, showing the cord compression, the T2 signal change within the cord (myelomalacia), and the degree of canal stenosis. The teaching point is that a normal Hoffman sign does not exclude cervical myelopathy, and the clinician who is reassured by a single negative physical sign in a patient with progressive gait disturbance or hand clumsiness has missed the diagnosis. The corollary is that the indication for an MRI is the clinical suspicion (progressive symptoms, combined UMN signs), not the positivity of any single bedside maneuver.