Putative paraneoplastic pemphigus and myasthenia gravis in a cat with a lymphocytic thymoma

Paraneoplastic pemphigus (PNP) is a rare and severe autoimmune blistering skin disease of humans. It is associated mainly with haematopoietic neoplasia and a unique autoantibody profile. At this time and in animals, PNP has only been reported in dogs.

To report clinical, histological and immunological findings in a cat with suspected thymoma-associated PNP.

An 8-year-old female spayed Himalayan cat.

The cat presented with a thoracic mass diagnosed as a lymphocytic thymoma. Two weeks postremoval, the cat developed myasthenia gravis, which was controlled with prednisolone and pyridostigmine. The myasthenia gravis resolved, but the cat developed severe cutaneous erosions and ulcers primarily affecting the caudal ventral abdomen and perineum, but also the ventral chest, axillae and medial pinnae. Histopathological analysis revealed changes consistent with pemphigus vulgaris and erythema multiforme, a combination of lesions highly suggestive of PNP. Direct immunofluorescence revealed intercellular epidermal IgG deposition in the lower epidermis, especially in areas of suprabasal clefts. Indirect immunofluorescence revealed antikeratinocyte IgG to basal keratinocytes and bladder epithelial cells. Immunological results supported a diagnosis of PNP. Skin lesions were treated with prednisolone and chlorambucil and, after clinical remission was obtained, the drugs were tapered and eventually discontinued without further recurrence of skin lesions.

In this cat, clinical, microscopic and immunological findings were consistent with a diagnosis of PNP, with thymoma being the suspected cause.