Glucagonoma : Pathophysiology
Pathophysiology of Glucagonoma: Unregulated production of glucagon by the tumor leads to high glucagon levels. Fasting plasma glucagon levels are usually <200 pg/ml. The levels in glucagonoma patients are markedly elevated ranging from 550 to 6600 pg/ml (mean 2110 pg/ml). Mild elevation of plasma glucagon levels (200 to 500 pg/ml) may be seen in many conditions, including cirrhosis, chronic renal disease, diabetic ketoacidosis, prolonged starvation, acute pancreatitis, acromegaly, hypercorticism, severe burns, severe stress, septicemia, and celiac disease. Hyperglucagonemia stimulates hepatic glycogenolysis and gluconeogenesis. The characteristic skin rash is thought to result from amino acid deficiencies created by accelerated amino acid oxidation and gluconeogenesis from amino acid substrates in the liver. Other nutritional deficiencies (e.g. zinc, essential fatty acids) resulting from altered metabolism may also contribute to skin rash. Weight loss is due to the catabolic effects of glucagon. In glucagon cell hyperplasia and neoplasia, mutations in GCGR gene result in decreased expression of glucagon receptors in the liver. The negative feedback loop between the liver and glucagon-producing cells in pancreas is broken, leading to glucagon cell hyperplasia and high glucagon levels. This photograph illustrates oral manifestations of glucagonoma, such as atrophic glossitis, angular stomatitis, and cheilitis. Image source: Dermnet NZ; used under license: Creative Commons Attribution-NonCommercial-NoDerivs 3.0 (New Zealand).