Glucagonoma

Description

Glucagonomas are very rare tumours of the alpha cells of the pancreatic islets of Langerhans that produce the hormone glucagon without appropriate regulation. The excessive secretion of glucogon is a form of topic paraneoplastic syndrome. The disease has been reported in ten dogs and it is therefore extremely rare.

As in humans, glucagonoma is characterised by the formation of skin lesions collectively described as necrolytic migratory erythema (NME), a syndrome which is observed much more commonly in dogs with liver failure when it is termed hepataocutaneous syndrome. Glucagonoma accounts for approximately ten percent of cases of NME. Dogs with glucagonoma frequently show signs of diabetes mellitus as glucagon is antagonistic to insulin.

Signalment

Glucagonoma has only ever been described in dogs and humans.

Diagnosis

Clinical Signs

Affected animals develop cutaneous signs of NME, comprising erosive, crusting lesions of:

• The feet and digital pads are the most common location
• The external genitalia
• The muco-cutaneous junctions of the mouth and eyes
• The distal extremities and other pressure points (elbows, hocks and ventral abdomen)
• The pinnae

Other clinical signs observed in dogs with glucagonoma are non-specific and include lethargy, anorexia, weight loss and lymphadenopathy.

Laboratory Tests

Affected animals often develop hypergylcaemia due to the effects of glucagon and it may be difficult to differentiate the disease from simple diabetes mellitus. Glycosuria may also be detected.

Excessive concentrations of glucagon are thought to increase the rate at which amino acids are converted to urea in the liver, reducing the plasma concentrations of amino acids.

Other reported changes on analysis of blood samples include increased ALP and ALT, decreased albumin and globulin and decreased blood urea concentrations.

In humans, serum glucagon concentration is measured to diagnose glucagonoma and this has also been reported in dogs.

Pathology

A definitive diagnosis is made by performing immunohistochemistry on pancreatic biopsy samples to detect an expanded population of glucagon-secreting alpha cells. The tumours are often large at the time of disgnosis (>5 centimetres in diameter) and they frequently metastasise to the liver or local lymph nodes. Vacuolar hepatopathy may be observed on histopathological analysis of liver biopsies.