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Q1: What is the diagnosis?
The diagnosis is a dopamine secreting phaeochromocytoma. The abdominal computed tomogram (p 124) shows a left adrenal mass (8 × 6 cm) with haemorrhagic and necrotic areas. A131I-metaiodobenzylguanidine scintigram showed uptake in the left adrenal gland.
A histopathologically proved benign phaeochromocytoma was resected. Immunohistochemical study revealed enhanced expression of tyrosine hydroxylase and low expression of dopamine β-hydroxylase in the tumour. These findings are consistent with the secretion of dopamine, as dopamine β-hydroxylase is the enzyme that synthesises norepinephrine from dopamine. An increased production of dopamine and homovanillic acid is uncommon with benign lesions but may occur with malignant phaeochromocytoma.1 Over a one week period her diarrhoea subsided. The plasma and urinary dopamine and urinary homovanillic acid concentrations returned to normal. Her blood pressure one week later was 140/80 mm Hg.
Q2: What is the cause of diarrhoea?
The cessation of diarrhoea after tumour resection suggests that dopamine may cause diarrhoea, perhaps via D1-like receptors in the gastrointestinal tract.2 Diarrhoea is an uncommon sole manifestation of phaeochromocytoma.3 A literature search revealed only one other report of dopamine secreting phaeochromocytoma presenting solely with diarrhoea.4
Box 1: Common mechanisms for loose motions in phaeochromocytoma
Ectopic production by phaeochromocytoma of: vasoactive intestinal peptide (watery diarrhoea, hypokalaemia, achlorhydria syndrome); serotonin; somatostatin; calcitonin.
In phaeochromocytoma as part of multiple endocrine neoplasia 2A and 2B syndromes; calcitonin, serotonin, and prostaglandin production from medullary thyroid carcinoma may lead to diarrhoea.
Phaeochromocytoma may be associated with gastrinoma of Zollinger-Ellison syndrome, leading to presentation with diarrhoea.
Q3: What is the cause for remission of her hypertension?
The dopamine receptors in peripheral tissues are of two functional classes: D1 and D 2-like receptor. Stimulation of postsynaptic,7 D1-like receptors or presynaptic D2-like receptors may cause vasodilatation.8 Stimulation of D1-A receptors promotes natriuresis and lowers blood pressure in humans.9 A deficient renal dopamine formation or action may contribute to hypertension,10 and a deficient dopaminergic response to salt loading may play an aetiological part in patients with a salt sensitive form of hypertension.11D1-A receptor deficient mice have been shown to have hypertension, suggesting a hypotensive action from dopamine.12 This is consistent with the spontaneous lowering of blood pressure initially and the increase in blood pressure after resection of dopamine secreting phaeochromocytoma seen in our patient.13
Two months after surgery she continues to be asymptomatic. Her blood pressure is 140/80 mm Hg. The urinary 24 hour catecholamines, dopamine, and homovanillic acid of the patient, her three siblings, and two sons were normal. The patient and her family are on regular follow up at the endocrinology outpatient clinic.
Dopamine secreting benign phaeochromocytoma.
Intractable diarrhoea may be the only manifestation of a dopamine secreting phaeochromocytoma