Differential sensitivity of thick and thin fibers to HIV and therapy-induced neuropathy

The study assessed HIV-related and anti-retroviral therapy-induced neuropathy in myelinated and unmyelinated nerve fibers. One hundred consecutive HIV patients were examined clinically and standard nerve conduction velocities were measured. In addition, electrically induced sympathetic skin response (SSR) was assessed in the palms and soles. The difference in delay of SSR in palms and soles (ΔSSR) was calculated as an indirect measure of C-fiber conduction velocity. Thick fiber conduction velocities significantly decreased with age and increasing stage of the disease, whereas no effect of stage was found for ΔSSR (p = 0.6). In contrast, medication of at least one of the most known neurotoxic drugs zalcitabine, stavudine, or didanosine did not result in significantly lower conduction velocities in thick fibers (51.29 ± 3.4 m/s vs. 50.86 ± 3.5 m/s), but was related to an increased ΔSSR. ΔSSR allows an indirect measurement of C-fiber conduction velocity. In HIV this measure of unmyelinated sympathetic fibers was most sensitive to anti-viral treatment whereas conduction velocity of myelinated somatic fibers was more sensitive to disease-related neuropathy. The results suggest that HIV neuropathy preferably affects myelinated and anti-retroviral therapy unmyelinated fibers.