Exclusive electrophysiological motor involvement in carpal tunnel syndrome.

OBJECTIVE: To define the frequency of exclusive electrophysiological motor involvement in carpal tunnel syndrome (CTS). METHODS: We reviewed the electrophysiological studies of 2727 consecutive hands with typical symptoms and signs of CTS and at least one abnormal test of the following: median distal motor latency (DML), digit two sensory conduction velocity (D2-SCV), segmental D2-SCV from wrist to palm, median-ulnar sensory latency difference from ring finger stimulation. RESULTS: Thirty-one hands (1.2%) had prolonged median DML ( > 4.4 ms) with normal SCV ( > 48 m/s). In 17 of 31 hands, segmental D2-SCV from wrist to palm or median-ulnar latency difference from ring finger stimulation were also performed with normal results in 8 hands, demonstrating a true exclusive electrophysiological motor involvement. CONCLUSIONS: In CTS, exclusive electrophysiological involvement of median motor fibers is rare. It may be related to preferential compression of the intraneural motor fascicles clumped superficially in the most volar-radial nerve quadrant or, more probably, to the fact that the recurrent thenar branch may exit the carpal tunnel through a separate ligamentous tunnel within the transverse carpal ligament where it may be preferentially or selectively compressed.

Low back pain due to hypertrophic roots as presenting symptom of CIDP.

Attention has recently been drawn to chronic inflammatory demyelinating polyneuropathy (CIDP) with symptomatic nerve root hypertrophy. A 31-year-old woman had fluctuating and worsening low back pain. Absent tendon jerks and a slight weakness of the hand interossei muscles suggested a diffuse neuropathy. The electrophysiological and histological findings were diagnostic for CIDP. Lumbar spine MRI showed marked nerve root enlargement with gadolinium enhancement. This case widens the range of the clinical presentations of CIDP. Further studies are warranted to ascertain whether cauda equina gadolinium enhancement may be a useful tool in the diagnosis of CIDP and a marker of disease activity for monitoring response to therapy.

Conduction block and segmental velocities in carpal tunnel syndrome.

In carpal tunnel syndrome (CTS) standard measurement of median distal motor latency and sensory conduction does not distinguish whether low amplitude responses are due to axonal degeneration or demyelination. In 88 control and 294 CTS hands we recorded amplitude and duration of compound muscle action potential (CMAP) and of antidromic sensory nerve action potential (SNAP) after palm and wrist stimulation to determine wrist to palm amplitude, duration ratios and segmental conduction velocities. In 16% of CTS hands there was an abnormal amplitude reduction without increased duration of CMAP or SNAP from wrist stimulation indicating partial conduction block. In 148 hands distal motor latency to abductor pollicis brevis and/or sensory conduction to digit 2 were abnormal. In the remaining 146 hands wrist to palm motor conduction was less than 35 m/s in 22.6% and wrist to palm sensory conduction was less than 45 m/s in 13%. At least one segmental conduction was abnormal in 27% of hands. Segmental studies allow the discrimination between conduction block and axonal degeneration, increase diagnostic yield in CTS, and might be useful in addressing treatment and predicting outcome.

Genetic regulation of light damage to photoreceptors.

Albino mice of different inbred strains have been exposed to constant fluorescent lighting at an illuminance level of 115-130 ft-c for intervals of 1-6 weeks. Under these conditions the photoreceptors in retinas of albino BALB/cByJ mice rapidly degenerate, whereas the photoreceptors in retinas of albino C57BL/6J-c2J mice are remarkably more resistant to light damage. F1 heterozygotes produced from these two strains display an intermediate degree of light-induced degeneration. These findings demonstrate that phenotypically identical populations with different genetic constitutions can show markedly different sensitivities to light, and that genetic factors must now be included as a determinant for the severity of light damage.

Strain differences in sensitivity to light-induced photoreceptor degeneration in albino mice.

The sensitivity to light-induced photoreceptor degeneration was examined in 7 different inbred strains of albino mice. The mice were exposed to 3 weeks of constant fluorescent light at an illuminance level of 115-130 ft-c (ca. 1,265-1,430 lux), after which the eyes were examined histologically. The degree of light-induced photoreceptor degeneration was compared to that found in BALB/cByJ (BALB/c) albino mice, which have previously been described as sensitive to the damaging effects of light, and to C57BL/6J-c2J albino mice, which have been shown to be resistant to light-induced damage. Mice of the A/J, AKR/J and NZW/LacJ strains were indistinguishable from BALB/c mice in light sensitivity, as measured by mean outer nuclear layer thickness and the presence or absence of outer segment membranes. Mice of the Ma/MyJ and RF/J strains were somewhat more sensitive to light than BALB/c mice, and those of the RIIIs/J were far more sensitive than all of the other strains. The LG/J strain differed from other strains by individual mice displaying one of two degrees of light sensitivity, those similar to the light-sensitive Ma/MyJ and RF strains and those remarkably more resistant to light, with photoreceptor outer segment integrity even greater than that of the light-resistant C57BL/6J-c2J strain. These findings demonstrate that different inbred strains of a given species may exhibit a wide range of sensitivities to constant light exposure and that most albino mouse strains examined thus far are highly sensitive to the damaging effects of light.