Comparison of CMT1A and CMT2: similarities and differences

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J Neurol. 2006 Aug 28

Comparison of CMT1A and CMT2: similarities and differences.

Bienfait HM, Verhamme C, van Schaik IN, Koelman JH, de Visser BW, de

Haan RJ, Baas F, van Engelen BG, de Visser M.

Dept. of Neurology, H2-222, Academic Medical Center, University of

Amsterdam, PO box 22660, 1100, DE, Amsterdam, The Netherlands,

To evaluate the clinical and electrophysiological similarities and

differences between two large groups of patients with Charcot-Marie-

Tooth disease, i.e. CMT1A and CMT2, we performed a post hoc

comparison of clinical and electrophysiological data.Most CMT1A and

CMT2 patients had the classical CMT phenotype. Age of onset was

significantly later in CMT2.

Total areflexia was present in approximately half of the CMT1A

patients whereas it was rare in CMT2. Foot deformities and weakness

of knee extensor and foot dorsal flexor muscles were more frequent in

CMT1A.

Median nerve motor nerve conduction velocities (MNCV) were always

less than 38 m/s in CMT1A patients, whereas this was also the case in

16% of the CMT2 patients. Sensory nerve conduction velocities showed

less overlap.

In both CMT1A and CMT2 CMAP and SNAP amplitudes were often reduced or

not obtainable in the legs. In CMT1A, SNAP amplitude was more reduced

and SNAP duration more prolonged than in CMT2.

We conclude that there are no robust clinical signs or symptoms that

differentiate between CMT1A and CMT2 patients. Electrodiagnostical

studies show a length-dependent motor and sensory axonal dysfunction

in both CMT-types. Additional SNAP and SNCV evaluation may be helpful

in focusing molecular genetic analysis in the occasional case of CMT2

showing slow motor nerve conduction velocities overlapping with CMT1A

values. The reduction of CMAP and SNAP amplitudes in CMT1A is

probably a combined effect of demyelination and axonal dysfunction.