Microscopic examination of the specimen revealed chronic inflammation and occasional microabcesses located in the dermis. Amorphous aggregates of filamentous bacteria (sulfur granules) were also seen. A smear of the granule showed an aggregate of filamentous, gram-positive bacteria, while a culture of the lesion yielded coagulase-negative Staphylococcus.
Mycetoma is a chronic, granulomatous infection of the skin and subcutaneous tissue caused by either aerobic bacteria (actinomycetoma) or fungi (eumycetoma).1,2 Actinomycetoma frequently occurs in tropical and subtropical regions, affecting the bare extremities of rural workers. The infection begins as a painless papule or subcutaneous nodule caused by the traumatic implantation of saprophytic bacteria. As the organism multiplies, the nodules grow and rupture internally to produce secondary lesions in the adjacent area.3,4 Deformity results as the infection spreads along fascial planes, producing tissue swelling and chronic sinus formation. These sinus tracts drain seropurulent material and sulfur granules. The color and morphological features of the grains provide clues to identify Actinomadura, Nocardia, or Streptomyces as the causal agent.2 Pain arises as the infection spreads to the underlying muscle or bone, while fever implies secondary infection.3,4
A Chronic Draining Plaque on the Foot. Arch Dermatol. 2002;138(10):1371–1376. doi:10.1001/archderm.138.10.1371