Epitheliotropic cutaneous lymphoma (mycosis fungoides) with formation of nodal and distant metastases in a dog: a case report

The presented case describes an interesting manifestation of epitheliotropic cutaneous lymphoma with formation of nodal and distant metastases in an 8-year-old cocker spaniel. Cutaneous lesions included multiple hypotrichous to alopetic foci, scales, erythematous plaques and multiple cutaneous nodules, often with superficial ulceration. The lesions were present predominantly on the neck, thorax, abdomen and hind legs. Clinically, the dog showed lethargy and there was an inappetence and a mild dyspnoe. Subsequent findings were generalized lymphadenopathy, fever, pallor of mucous membranes and tachycardia. Smear impression of cutaneous nodules contained degenerated neutrophils with phagocytized cocci and macrophages. Cytological examination of nodules (FNA) showed a predominantly round cell population, with a compound of histiocytoid cells mixed with cells of inflammatory infiltration. Histopathological examination of the skin was performed. There was infiltrate of large neoplastic round cells in the superficial and deep dermis, morphologically resembling histiocytes. In some tissue sections the neoplastic infiltrate was present only in the superficial dermis, composed of medium-sized lymphocytes with hyperchromatic round, oval to indented nuclei 1.5 red cells in diameter and a small amount of eosinophilic cytoplasm. Focal exulceration, formation of Pautrier's microabscesses in epidermis, and in some sections subepidermal and intraepidermal vesiculopustules and intraepidermal vesicles were present. Neoplastic infiltrate was CD3, CD18 and vimentin positive. Examination for CD79 and CD117 was negative. MHC II positivity was found only focally in cells of inflammatory infiltration in superficial dermis. Diagnosis of epitheliotropic cutaneous lymphoma (mycosis fungoides) was carried out. The response to the therapy of the disease was poor and the dog died two months after diagnosis. Necropsy revealed generalized lymphadenopathy, several white, fat-like nodules in heart muscle, lungs, esophagus and stomach, and mild hepatomegaly and splenomegaly. Multiple white disseminated foci were found in the spleen. Histopathological examination showed round cell, CD3 positive neoplastic infiltrate in heart, lungs, spleen, liver, lymph nodes, esophagus and stomach, morphologically corresponding with neoplastic infiltrate found in skin.