Cytomorphological patterns of Nerve aspirates in Pure Neuritic Leprosy-A single centre cross-sectional observational study

Background: Pure neuritic leprosy (PNL) poses a diagnostic challenge because of absence of skin patches, inconclusive skin biopsies and nerve conduction studies. Nerve biopsy though the diagnostic gold standard, is invasive, requires expertise, and may not be feasible in all cases. Fine needle aspiration cytology (FNAC) of accessible thickened nerves can be utilized as a minimally invasive diagnostic modality in PNL. This study was carried out to describe cytomorphological patterns of nerve aspirates in patients of PNL for diagnosis and classification of leprosy and study its advantage, if any, over skin biopsy. Methods: Twenty-seven treatment naive clinically diagnosed patients of PNL were included in this cross-sectional study carried out from January 2017 to December 2018 at a tertiary care centre in Western India. FNAC was done from a clinically involved nerve and aspirates were evaluated for cytomorphological characteristics and the presence of Acid-Fast Lepra bacilli. Results: Nerve aspirates were diagnostic in 10 (37%) patients while 17 (63%) aspirates showed non-specific or no inflammation. Of the diagnostic aspirates, six (22.2%) were classified as tuberculoid leprosy, three (11.1%) as lepromatous and one (3.7%) as borderline leprosy. Mycobacterium leprae were demonstrated among three (11.1%) of these aspirates. In comparison, only three (11.1%) skin biopsies were diagnostic of leprosy with features of indeterminate spectrum. Remaining 24 skin biopsies showed normal histology in 20 (74.1%) cases to perivascular lymphocytic infiltrate in four (14.8%) cases. Conclusion: Our study demonstrates that FNAC of clinically thickened nerves has a better diagnostic yield than skin biopsy in PNL and shows all spectrums of leprosy. It also offers the advantage of sampling major nerve trunks without the fear of residual neurological deficit. However, most of the smears were paucicellular and a negative aspirate does not rule out leprosy.