A Retired Electrician Whose Hand Weakness Is Not in His Neck
Mr. R is a 61-year-old right-handed retired electrician referred for 11 months of progressive right hand weakness. He can no longer turn keys or open jars, and for 4 months has tripped over his left foot. Examination shows atrophy of the right thenar eminence and first dorsal interosseous, visible tongue fasciculations, a brisk jaw jerk, sustained ankle clonus bilaterally, an extensor plantar response on the right, and a preserved right biceps reflex despite 4/5 elbow flexion. Cervical spine MRI shows C4-5 and C5-6 disc-osteophyte complexes with moderate bilateral foraminal stenosis and no cord signal change. Nerve conduction studies show normal right sural, radial, and median sensory responses, while median and ulnar CMAPs are reduced to roughly 40% of the lower limit of normal. Needle EMG shows active denervation with chronic reinnervation in the right first dorsal interosseous, right biceps, thoracic paraspinals at T6-T8, and right tibialis anterior; the right vastus lateralis is normal. He asks whether a cervical fusion will restore his grip.
1. Do these electrodiagnostic findings localize to the cervical spine, and does cervical spondylosis account for the whole picture? Walk through the reasoning that a board examiner would expect.
Read the worked answer
The findings do not localize to the cervical spine.
- Normal upper-limb SNAPs with reduced CMAPs indicate motor axon loss with an intact sensory ganglion. A root or plexus lesion severe enough to cause this degree of weakness would drop the corresponding SNAP, because the lesion would lie distal to the dorsal root ganglion or damage it.
- The needle EMG spans three spinal regions: cervical (first dorsal interosseous, biceps), thoracic (T6-T8 paraspinals), and lumbar (tibialis anterior). C4-6 spondylosis cannot denervate thoracic paraspinals or a tibialis anterior.
- The thoracic paraspinal finding is the highest-yield data point. It lies outside any limb and outside the cervical spine, so it converts an apparently focal problem into a widespread process.
The preserved biceps reflex alongside jaw jerk, clonus, and an extensor plantar response gives upper motor neuron signs in bulbar and lumbar regions; tongue fasciculations give lower motor neuron bulbar signs. With LMN signs in cervical, thoracic, and lumbar regions plus UMN signs, this satisfies clinically definite ALS under the revised El Escorial criteria.
His foraminal stenosis is a bystander: degenerative change is nearly universal at 61, and imaging abnormalities do not produce thoracic paraspinal fibrillations. Beware the trap of treating the MRI rather than the patient.
2. What do you recommend regarding the proposed surgery, the remaining workup, and how you counsel him?
Read the worked answer
Recommend against cervical fusion. Tell him plainly that decompression will not restore grip and could trigger a perioperative crisis: ALS patients have elevated risk of aspiration, prolonged ventilation, and accelerated functional decline after major surgery. Offer a second opinion if he wants one; do not simply refuse.
Exclude treatable mimics before finalizing the diagnosis:
- Vitamin B12, TSH, comprehensive metabolic panel, CK, SPEP with immunofixation, HIV.
- MRI brain if any atypical feature (sensory level, eye movement abnormality, prominent cognitive change).
- Anti-GM1 only if conduction block is present - there is none here, so multifocal motor neuropathy is not supported.
Genetic testing with practical consequences:
- C9orf72 expansion: prognostic and family counseling implications.
- SOD1: eligibility for targeted therapy, so this should not be deferred.
Baseline and ongoing care: seated and supine FVC, maximal inspiratory pressure or SNIP, ALSFRS-R, speech and swallow evaluation. Start riluzole and discuss other disease-modifying options, refer to a multidisciplinary ALS clinic, arrange PT/OT and home safety assessment, and open advance care planning early while he can participate.