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Case Reports

Abstract

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a distinct single or multisystemic histiocytic disorder characterized by ALK immunoreactivity and ALK rearrangements, most commonly KIF5B-ALK fusions.

We present a complicated case of diffuse cutaneous ALK-immunoreactive histiocytosis without ALK rearrangement in a 37-year-old woman in the setting of syphilis and histoplasmosis. The patient presented with clinically impressive indurated yellow, pink, and skin-colored papulonodules on the face, chest, back, and upper arms.  Histopathologically, punch biopsy revealed an extensive dermal histiocytic infiltrate with many Touton giant cells and xanthomatous features with positive immunoreactivity to ALK, CD163, S100, cyclin D1, and Oct2. Cytogenetics analysis failed to detect ALK rearrangement. The patient’s RPR was positive, however, anti-treponema pallidum immunohistochemical studies failed to detect organisms. Treatment with benzathine penicillin was initiated.  Further imaging with PET-CT revealed diffuse cutaneous involvement and several prominent lymph nodes in the upper neck. Right deep cervical lymph node biopsy revealed numerous intracellular microorganisms present on GMS stain suggestive of histoplasmosis; however, tissue cultures were negative. Diagnoses of histoplasmosis and ALK-immunoreactive histiocytosis were made. The Patient underwent a course of amphotericin for histoplasmosis. The ALK inhibitor, alecitinib was started for the ALK-immunoreactive histiocytosis. At her most recent clinic visit, the patient’s skin lesions were responding and improving after 3 months on alecitinib.

Our case highlights the importance of testing for ALK expression by immunohistochemical and molecular methods in unusual histiocytic proliferative disorders for better identification and treatment of this disease. Further molecular studies are necessary to examine for unknown ALK rearrangement in ALK-immunoreactive histiocytosis.