Necrobiosis lipoidica and cutaneous anaesthesia: immunohistochemical study of neural fibres.

BACKGROUND Cutaneous anaesthesia in necrobiosis lipoidica (NL) has been attributed to the destruction of nerve fibres by the inflammatory process. In the 1980s, one study demonstrated a decrease in S100 positive neural fibres as proof of this. Thermalgic information is mainly dependent on small fibres, either myelinated or unmyelinated, and S100 protein is expressed by Schwann cells. OBJECTIVE We designed an immunohistochemical study with anti-neurofilament and peripherin in 5 cases of NL, in order to investigate if there was a decrease of axons in NL. METHODS We reviewed 5 cases of NL and performed an immunohistochemical study on all of them, with neurofilaments and peripherin antibody in sections of 4 microm. Slides were examined under a conventional light microscope, and we searched for the presence of fibres in the necrobiotic areas, as well as in the periphery of the necrobiotic areas. Controls for both markers were also used. RESULTS The median number of nerve fibres in the control biopsies was 5.2 per mm2. The nerve fibres were absent in the central part of the necrotic foci, and only scattered fibres were evidenced in the periphery of the foci. Myelinated nerve trunks seemed to be hypertrophied in the areas located between the necrotic foci. CONCLUSIONS The absence of nerve fibres in the central areas of the necrotic foci of NL might explain the anaesthesia which is present in many patients with that disease.