O3 Nerve conduction studies in small fibre neuropathies. a service evaluation study

Abstract

Objectives To evaluate the relation between NCS results and skin biopsies in patients with small fibre neuropathy. Small fibre neuropathies are a special type of peripheral nerve pathology that affects specifically the thinly myelinated or non myelinated fibres. Ancillary diagnostic tests are usually necessary to make an adequate diagnosis. Among them the most widely used in the skin biopsy, based on the intraepidermal nerve fiber density test (IENFD). Normalised values for this parameter exist for different ages and sexes. Nerve conduction studies are supposedly unhelpful to diagnose these conditions. Methods Our study looked at the results of the nerve conduction studies performed in patients who underwent a skip biopsy looking for IENFD. Results 34 patients were found in our database. Of those only 8 had an abnormal NCS result, and only 2 patients had an abnormal IENFD and an abnormal NCS. These abnormalities were circumscribed to focal entrapment neuropathies. Discussion We found that nerve conduction studies had a negative predictive value of 0.875, confirming the widely held opinion that normal nerve conduction studies are a requisite for the diagnosis of small fibre neuropathy. Conclusions Since large and small fibre neuropathies share many similar etiologies we expected to see more abnormal NCS results in patients with abnormal IENFD. Significance In summary our results seem to suggest a different natural history and pathophysiology for large and small fibre neuropathies.