A case of primary cutaneous nocardiosis presenting as unilateral papulopustular eruption in an immunocompetent host.

Primary cutaneous nocardiosis is often challenging to diagnose in a timely manner due to its diverse and nonspecific clinical manifestations, compounded by the difficulty in culturing and identifying Nocardia species. This case report describes a patient with primary cutaneous nocardiosis caused by Nocardia brasiliensis, who presented with normal immune function and no significant history of trauma. The patient initially developed blood blisters on the ankle, which then spread to papules and pustules throughout the entire left lower limb. Through repeated secretion of bacterial cultures and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) technology, the Brazilian Nocardia species was identified and subsequently treated with trimethoprim-sulfamethoxazole (TMP-SMX). This case underscores the importance of repeated microbiological testing and the use of advanced diagnostic techniques, including MALDI-TOF-MS, when confronted with atypical infectious symptoms. It also highlights the critical role of early diagnosis and treatment in improving patient outcomes.