Concomitant erythema multiforme in a dog with small-cell T-cell intestinal lymphoma: coincidence or paraneoplastic syndrome?

Erythema multiforme is a rare immune-mediated cutaneous disorder. Canine erythema multiforme (EM) can occur secondarily to triggers such as drugs, food and infections but is more commonly considered idiopathic. In humans, a paraneoplastic origin is also described whereas paraneoplastic EM has only been reported in one dog with thymoma. This case report is the first description of a dog with EM concurrently diagnosed with low-grade small-cell T-cell intestinal lymphoma, raising the suspicion of a paraneoplastic syndrome. A 9-year-old, neutered male, crossbred dog, with no history of travel outside the United Kingdom or recent drug administration presented with progressive cutaneous lesions, pyrexia, lethargy, vomiting, and weight loss. Cutaneous lesions were generalised and consisted of multifocal to confluent erythematous macules and focally extensive variably sized patches of moderate to severe erythema and crusting, with ulceration. Histopathology was consistent with EM. Computed tomography identified a jejunal mass associated with jejunal lymphadenomegaly. The intestinal mass was excised and the enlarged non-resectable lymph node was biopsied. Histopathology, immunohistochemistry and PCR for antigen receptor rearrangement were consistent with transmural small-cell low-grade T-cell intestinal lymphoma with nodal involvement. Methylprednisolone and chlorambucil were initiated leading to complete resolution of the dermatological and gastrointestinal signs. Both drugs were progressively tapered and discontinued. During and post-treatment, repeat abdominal imaging with cytology and flow cytometry of the persistently mildly enlarged jejunal lymph node showed no evidence of lymphoma. Six months following chlorambucil discontinuation there was a recurrence of the cutaneous lesions with severe systemic deterioration, suggesting EM relapse. No triggers were identified. Repeat staging was declined and euthanasia was performed, 26 months following initial diagnosis. This is the first case reporting the concomitant occurrence of EM and small-cell lymphoma in a dog. While the relationship between these two diseases remains uncertain, a paraneoplastic disease was possible. This case highlights the importance of thorough investigations when canine EM is diagnosed, and an idiopathic origin is suspected.