Actinomycosis and nocardiosis. A morphologic study of 17 cases.

Actinomycosis and nocardiosis are bacterial infectious diseases with distinct morphologic features, that can be diagnosed in tissue sections. The clinico-pathologic features of 17 cases are reported with emphasis on their histopathologic diagnosis by using a simple combination of common tissue stains. Actinomycosis was frequently observed as a secondary and localized infection often with lung involvement, especially in residual cavities or bronchiectasis; in these cases numerous actinomycotic granules and only occasionally individual bacterial filaments within the suppurative foci and/or granulomas with suppurative centers were identified. Nocardiosis was observed as an opportunistic infection in the three cases studied; in these, isolated filaments of acid-fast and Gram-positive bacteria were observed. The morphologic features and the differential diagnosis in tissue sections of both infections are discussed with emphasis on their identification by the general pathologist in the routine material.