Bullous amyloidosis in a horse: first description in veterinary medicine

Bullous amyloidosis is a rare disease in humans that has not been described in a veterinary species in the peer-reviewed literature. The human disease is characterised by haemorrhagic vesicles and bullae on the skin and mucosae, which form due to amyloid deposition.

To describe the clinical features, laboratory analysis and histopathological features of an unique presentation of bullous disease in a horse.

A 17-year-old thoroughbred mare presented for weight loss and severe oral cavity ulcers.

Investigations involved haematological evaluation, chemistry profiles, gastroscopy and serum protein electrophoresis, and, postmortem, histopathological evaluation, Congo-red staining and transmission electron microscopy (TEM).

Haemorrhagic vesicles and bullae occurred on the mucosa of the oral cavity, lips, oesophagus and stomach, and much less the muzzle, face and mucocutaneous areas of the perineum, where scarring was evident. Histopathological evaluation and Congo-red staining confirmed the presence of amyloid deposits in dermis and submucosa, in association with vesicle and bulla formation, consistent with bullous amyloidosis. TEM confirmed amyloid fibril deposition in the dermis and along the basement membrane zone. Clefts occurred in the superficial dermis and submucosa, which explained haemorrhage and scarring. The presence of a polyclonal gammopathy and the rapid abolishment of Congo-red staining with performate pretreatment supported serum amyloid A and secondary amyloidosis.

Bullous amyloidosis is a novel disease of the horse and a newly recognised differential for bullous disease, for which the haemorrhagic nature of bullae, scarring and deep secondary ulcers are considered clinical clues to the condition.