An underrated differential diagnosis for subcutaneous lumps: 26 cases of subcutaneous Dirofilariasis

Abstract

IntroductionEven though subcutaneous dirofilariasis [worm granuloma] is an emerging zoonosis, it is not commonplace to consider it as a differential diagnosis for a subcutaneous lump even in the endemic zones. Moreover, the available literature lacks attempts to provide a unified clinical profile for it to be considered as a clinical entity.Methods We have retrospectively analyzed patients who were diagnosed with subcutaneous dirofilariasis at a Base Hospital in the Uva Province of Sri Lanka from February 2018 to March 2020. We evaluated patient demographics, symptomatology, clinical signs, ultrasonographic and histopathological features.Results Twenty-six patients with a mean age of 15.6 years [range 1 – 67 years] were analyzed. The locations of the lumps were highly variable, the commonest being the abdominal wall [34.6%]. Most [84.6%] were asymptomatic. The average diameter was 14.2mm [range 8 – 25mm]. The majority were neither tender nor warm, firm, and had ill-defined margins and a smooth surface without fluctuation, transillumination, or slipping sign. All were in the subcutaneous plane often attached to the deep fascia but without attachment to the skin. Blood investigations were unremarkable with a normal ESR and eosinophil count. The ultrasonographic finding was an echogenic tubular structure within a hypoechoic lesion. Histopathology demonstrated a worm surrounded by granulomatous inflammatory infiltrates with eosinophils and lymphocytes. Conclusion We emphasize the importance of regarding subcutaneous dirofilariasis as a differential diagnosis for subcutaneous lumps, especially in the highly prevalent geographical zones to minimize 'incidental diagnosis'.