A previously undescribed cutaneous paraneoplastic syndrome in a cat with thymoma

Exfoliative dermatitis is a well-recognized cutaneous paraneoplastic syndrome (PNS) associated with thymoma in cats, of which the clinical and histopathological presentation has been well-characterized.

To describe a novel clinical skin manifestation associated with thymoma in a cat.

A 14-year-old neutered female domestic short hair cat.

Physical, abdominal ultrasonographic, thoracic radiographic, ultrasonographic and computed tomographic examinations, histopathological assessment of the skin and mediastinal mass.

The cat was presented with noninflammatory alopecia, with a dorsal multifocal distribution. Examination of the alopecic areas using a dermascope indicated an apparent lack of follicular ostia. Histopathological assessment of alopecic areas confirmed follicular and epidermal atrophy, trichilemmal keratinization and mild orthokeratotic hyperkeratosis. Diagnostic imaging revealed a mediastinal mass, which was surgically removed. Histopathological and immunohistopathological examination of the mass was consistent with a thymoma, associated with multiloculated cyst formation and multifocal cholesterol granulomas. Following surgery, hair re-growth was noted in the previously alopecic areas. The cat was euthanized 3.5 months later because of recurrent chylothorax suspected to be a postoperative complication. The alopecic lesions had improved markedly.

Thymoma-associated PNS might not always manifest as an exfoliative dermatitis and should be considered in the differential diagnosis of multifocal noninflammatory alopecia.