S12C12bP2b-AFB: M. marinum infection

S12C12bP2b-1: This lesion of the hand shows hyperkeratosis and acanthosis of the epidermis. Activated histiocytes form compact infiltrates in the upper portion of the reticular dermis. The infiltrates are rather uniform. A cleft between the infiltrate and the papillary dermis contains extravasated red blood cells.

S12C12bP2b-2: Neutrophils are loosely sprinkled among the histiocytes.

S12C12bP2b-3: Histiocytes form confluent infiltrates in the subcutaneous fat. Lymphocytes are loosely sprinkled among the histiocytes. To the right near the top of the field, there is a small collection of multinucleated giant cells.

S12C12bP2b-4: In the dermis, on some of the sections, there are areas of suppuration; in these areas, the monotonous pattern of the histiocytic infiltrates is interrupted. The patterns are suppurative and granulomatous; this combination of features is most characteristic of an infectious process. The extremity of a column of invasive, benign squamous epithelium (i.e., pseudo-epitheliomatous hyperplasia) abuts upon the area of suppuration.

S12C12bP2b-5: Squamous epithelium has invaded the dermis and is in contact with the zone of suppuration. The epithelium has extended into the reticular dermis; the epithelial patterns qualify as pseudo-epitheliomatous hyperplasia. The “claw-like” configuration of the epithelial extremity is a common feature of pseudo-epitheliomatous hyperplasia, as seen in the “perforating disorders.”

S12C12bP2b-6: The rather diffuse and monotonous infiltrates of histiocytes are somewhat unusual.

 

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