Background: Lichenoid and granulomatous dermatitis defines a distinctive pattern of cutaneous inflammation that may be part of the morphologic spectrum of idiopathic lichenoid reactions such as lichen planus and as well may be seen with lichenoid drug reactions, endogenous T-cell dyscrasias and as a feature of certain systemic diseases especially Crohn's disease and rheumatoid arthritis.
Results: We encountered three cases of lichenoid and granulomatous dermatitis in which the basis was one of primary cutaneous Mycobacterium infection. In all three cases acid fast stains revealed pathogenic organisms and as well cultures were positive for Mycobacterium kansasii in one case and Mycobacterium marinum in another. Other features included a prominent perineural and periadnexal lymphocytic infiltrate.
Conclusions: The differential diagnosis of lichenoid and granulomatous dermatitis should also encompass primary cutaneous Mycobacterium infection in addition to the other more characteristic entities associated wtih this distinctive reaction pattern. Infection with Mycobacterium induces a TH1 dominant response which would hence produce an infiltrate.