Cytomorphological spectrum and immunochemistry of cutaneous tuberculosis

Objectives The diagnosis of cutaneous tuberculosis is challenging due to its diverse clinical manifestations, paucibacillary state and lack of proper diagnostic tests. Clinico‐pathological correlation is still frequently used for diagnosis. There is paucity of literature on cytomorphological features. Immunochemistry can help as an ancillary test. Methods Clinical diagnosis was made after thorough history and physical examination. Modified Fine Needle Aspiration technique was used to collect cytology samples and 3 mm punch biopsy for histological examination. Findings on histopathology were compared with cytomorphology. Immunochemical staining with anti‐TB polyclonal antibody using standard Polymer‐based‐HRP immunochemistry technique and comparison of cytology and histology findings. Results The morphological spectrum of biopsy and cytology showed high correlation using nine parameters: necrosis, granulomas, giant cells, AFB, neutrophilic infiltrate, presence of lymphocytes, histiocytes, collagen bundles, and immunochemistry. Diagnostic correlation of FNA compared to biopsy was found to be 90.3%. On comparing cytomorphology of scrofuloderma and lupus vulgaris, all the parameters were found more frequently in scrofuloderma except for granulomas, giant cells and immunochemistry. Immunochemistry showed sensitivity and specificity of 90.3% and 70% on biopsy, respectively, compared to 67.7% and 60% on FNA, respectively. Combined sensitivity of IHC and ICC was 96.8%. Conclusions The cytomorphological spectrum of cutaneous tuberculosis is comparable to clinicohistopathology with a high correlation of 90.3%. However, sub classification on FNA is difficult on cytology alone. While FNAC is a better diagnostic tool for finding AFBs hence confirming the diagnosis, biopsy is better for immunochemistry. Thus, biopsy and FNA complement each other.