History
Mr. Chow was a 70-year-old non-drinker who presented with a 2-year history of progressive paresthesia in a stocking- then glove-distribution with unsteady gait.
Physical examination
Normal limb power with generalized hyporeflexia, broad-based gait, and abnormal Romberg’s test.
Investigations
NCT:
- Markedly prolonged median and ulnar motor distal latencies (>10ms) with slowed motor conduction velocities and relatively preserved CMAP amplitudes.
- Sensory onset latencies and conduction velocities were disproportionately abnormal compared to SNAP amplitudes.
- Prolonged F-wave latencies and reduced persistence.
- No conduction blocks or temporal dispersion.
- Absent motor or sensory responses in the lower limbs.
Mildly elevated IgM levels with increased kappa free light chain.
CSF:
- Protein 1.6g/L, WCC and glucose normal
Thought process
Syndrome:
- Chronic, progressive, length-dependent, demyelinating polyneuropathy with predominantly sensory deficits including sensory ataxia.
Localization:
- Peripheral nerves.
- Specifically the distal segments (distal acquired demyelinating symmetric neuropathy).
Etiology:
- Inflammatory: anti-MAG in the setting of IgM paraproteinemia; other inflammatory neuropathies including paranodopathy.
- Paraneoplastic
Learning point:
- There absent lower limb responses on NCT gave me the impression of an axonal polyneuropathy (only the lower limbs were tested initially).
- Yet an axonal pathology was unable to account for the degree of abnormality in the latency or conduction velocity.
Useful reference:
- Limits on DL prolongation (less than 130% of ULN) and CV reduction (less than 75% of LLN) in severe axonal loss. Beyond that it usually indicates some significant degree of demyelination.
- Median DL >9ms CV <35ms.
- Ulnar DL >7ms CV <35ms.
- Tibial DL >12ms CV <30ms.
- Peroneal DL >14 ms CV <30ms.
- In cases with both demyelinating and axonal pathology, work up as demyelinating polyneuropathy.
Outcome
Anti-GM1 IgG strongly positive.
- MMN: almost exclusively motor deficits, anti-GM1 IgM positive .
- CIDP: motor deficits predominance, no association with specific antibodies.
- Anti-MAG: may demonstrate IgM with poly-reactivity in the setting of IgM paraproteinemia (ie false positive due to cross reactivity), but IgG was positive in your case.
Pending antibody testing.