Intermittent functional pheochromocytoma in a 26-year-old pony

Pheochromocytoma is a tumour of the chromaffin cells of the adrenal medulla. These tumours can be asymptomatic or functional, due to the secretion of catecholamines. Clinical signs associated with functional pheochromocytomas are mainly tachycardia, hyperlactataemia, hyperglycaemia and haemoconcentration. In this case report, we describe a 26-year-old pony gelding admitted to the Emmeloord Equine Clinic with multiple adrenergic crises, epistaxis, oesophageal obstruction and endocrinopathic laminitis with confirmed insulin resistance. In between these admissions, the pony competed successfully at national level. The final and fatal adrenergic crisis started with a behavioural change followed by profuse sweating. The pony showed haemoconcentration, hyperlactataemia and hyperglycaemia. Treatment with balanced isotonic fluids, pergolide, insulin and acepromazine failed to stop the worsening clinical state of the pony, and a decision for euthanasia was made. On post-mortem examination, the diagnosis of pheochromocytoma was confirmed. Due to the intermittent presence of clinical signs, the diagnosis intermittent functional pheochromocytoma was made.