A case of chronic, progressive distal weakness, numbness, and muscle wasting diagnosed as demyelinating polyneuropathy.

History.

Mr. Leung was a 70-year-old non-drinker who presented with a 5-year history of progressive distal tetraparesis, numbness, and hand small-muscle wasting.

PMH: NPC 1999 with RT, known right LMN facial weakness, hearing impairment, and tongue deviation likely secondary to post-RT status.

He had an elder brother who suffered from small-muscle wasting of the bilateral hands.

Physical examination.

Muscle wasting at the bilateral hands and feet with claw hands, pes cavus, and claw toes. Symmetrical distal tetraparesis with generalized hyporeflexia, broad-based gait, failed tandem walking, and abnormal Romberg. No limb ataxia or cord signs.

Investigations.

NCT:

  • Right median nerve: marked DL (16) and CV (21) prolongation, relatively preserved CMAP (9), absent sensory responses.
  • Right ulnar nerve: marked DL (11) and CV (17) prolongation, marked CMAP reduction (3), absent sensory responses.
  • No conduction block / temporal dispersion.
  • Other UL / LL nerves showed absent motor and sensory responses.

EMG:

  • Right FDI: inactive neurogenic changes
  • Right deltoid, biceps, triceps, EIP: normal

Thought process.

Syndrome:

  • Chronic, progressive, symmetrical, distal tetraparesis, paresthesia, muscle wasting, and sensory ataxia.

Localization:

  • Peripheral nerves
  • Uniform demyelination across distal and proximal segments (no CB / TD, not DADS)

Etiology:

  • Genetic (longstanding duration, skeletal deformities, suspected family history; CMT1A [demyelinating, not CMTX1 / HNPP], less likely vATTR neuropathy [no skeletal deformities, axonal pathology])
  • Autoimmune (paranodopathy, atypical CIDP [sensory predominance, no CB / TD])
  • Indolent infections (syphilis, HIV)
  • Metabolic (B12 deficiency, hypothyroidism)
  • Toxic (less likely, axonal)
  • Neoplastic / paraneoplastic (less likely, protracted clinical course, axonal)

Learning point:

  • Second encounter with diffuse absent responses on NCT (think axonal) but, in fact, marked demyelinating features in the remaining recordable nerves. The report was concluded as axonal polyneuropathy.
  • Recall the cutoffs for demyelinating changes not accountable solely secondary to axonal degeneration.

Next steps.

  • Blood tests (including paranodapathy panel)
  • CSF tests
  • MRI LS plexus (hypertrophy, enhancement)