Abstract
Cutaneous lymphocytosis (CL) is an uncommon and controversial lymphoproliferative disorder described in dogs and cats. CL is generally characterized by a heterogeneous clinical presentation and histological features that may overlap with epitheliotropic lymphoma. Therefore, its neoplastic or reactive nature is still debated. Here, we describe clinicopathological, immunohistochemical, and clonality features of a retrospective case series of 19 cats and 10 dogs with lesions histologically compatible with CL. In both species, alopecia, erythema, and scales were the most frequent clinical signs. Histologically, a dermal infiltrate of small to medium-sized lymphocytes, occasionally extending to the subcutis, was always identified. Conversely, when present, epitheliotropism was generally mild. In cats, the infiltrate was consistently CD3+; in dogs, a mixture of CD3+ and CD20+ lymphocytes was observed only in 4 cases. The infiltrate was polyclonal in all cats, while BCR and TCR clonal rearrangements were identified in dogs. Overall, cats had a long-term survival (median overall survival = 1080 days) regardless of the treatment received, while dogs showed a shorter and variable clinical course, with no evident associations with clinicopathological features. In conclusion, our results support a reactive nature of the disease in cats, associated with prolonged survival; despite a similar histological picture, canine CL is associated with a more heterogeneous lymphocytic infiltrate, clonality results, and response to treatment, implying a more challenging discrimination between CL and CEL in this species. A complete diagnostic workup and detailed follow-up information on a higher number of cases is warrant for dogs.
Highlights
Canine and feline cutaneous lymphocytosis (CL) is an uncommon lymphoproliferative disorder, sharing clinical and histological similarities with the human counterpart, for which etiology and pathogenesis are not completely understood [1,2]
From 2009 to 2020, 19 cats and 10 dogs with a histopathological diagnosis of Cutaneous lymphocytosis (CL) have been included in the study
We describe here a case series of 19 cats and 10 dogs diagnosed with CL according to previously established histopathological criteria [4,5,7]
Summary
Canine and feline cutaneous lymphocytosis (CL) is an uncommon lymphoproliferative disorder, sharing clinical and histological similarities with the human counterpart, for which etiology and pathogenesis are not completely understood [1,2]. Chronic inflammatory disorders are mainly characterized by a diffuse homogenous lymphocytic infiltrate, while cutaneous epitheliotropic lymphoma (CEL), varying among different forms, shows a peculiar tropism for epithelial structures of the neoplastic cells as a key diagnostic feature, and a varying degree of lymphocytic dermal infiltration, going from minimal and superficial to diffuse and nodular [7]. While initially considered the gold standard to differentiate cutaneous reactive disorders (polyclonal) from CEL (clonal) [9,10,11], recent studies have revealed contradictory data including clonal populations showing unexpected spontaneous regression and polyclonal populations progressing to overt lymphoma, thereby questioning its clinical utility [7,12]. Due to the rarity of CL and the difficulty in predicting its clinical behavior, the aims of this retrospective study were (i) to describe clinical, histological, and immunohistochemical features of 19 feline and 10 canine cases histologically compatible with CL and (ii) to correlate PARR results with clinical data
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