Pure neural leprosy: Diagnostic value of the polymerase chain reaction

Pure neural leprosy (PNL) is often difficult to diagnose when acid-fast bacilli (AFB) cannot be detected. We undertook the present study to evaluate use of the polymerase chain reaction (PCR) in diagnosing PNL. Fifty-eight patients (41 men and 17 women) suspected of pure neural leprosy (PNL) were examined. Patients were classified as borderline tuberculoid (BT, 40 cases) and polar tuberculoid (TT, 18 cases) types. Nerve biopsy was performed and was positive for AFB in 20 patients (all BT patients), i.e., 34.5% of total cases. DNA was extracted from the nerve biopsy samples and amplified using PCR for a specific repeated sequence of DNA from Mycobacterium leprae. PCR analysis was positive in the nerve samples from 29 patients (50%), 27 of the BT type, and 2 of the TT type patients. Further, PCR analysis was positive in 14 of 38 cases that were negative for AFB by nerve biopsy, of which 12 were of the BT type and 2 the TT type. PCR analysis proved to be a useful method to investigate pure neural leprosy, enabling confirmation of the diagnosis in more than a third of the cases that were negative for AFB by nerve biopsy.