Endocrine Abstracts

Introduction: Central diabetes insipidus (CDI) results from a deficiency of arginine vasopressin (AVP) secretion. It is treated by replacement therapy with the synthetic AVP analogue desmopressin. With atrial distension there is increased afferent vagal stimulation that decreases renal sympathetic tone and inhibits antidiuretic hormone (ADH) release, which in turn leads to the diuresis response. Additionally, atrial distension leads to atrial natriuretic peptide (ANP) release, which has powerful diuretic and natriuretic properties.

Case presentation: 25 year male presenting with polyuria of 5 litres daily for 1.5 years not preceded by head trauma, surgery, convulsions nor drug intake.

Physical examination: BP: 140/90 mmHg, Pulse: 58 b/m with frequent irregular irregularity, BMI: 23.3, normal RR and temperature. Unremarkable abdominal, neurological, chest and cardiological

Investigations: Normal CBC, liver kidney functions., Calcium, potassium, and thyroid function HbA1C: 4.4%, Serum osmolality: 279 mOsm/kg (275 to 295), serum sodium: 144 mmol/l (135-145) Urine specific gravity:1015, urine osmolality: 287 mOsm/kg (500-800), urinary sodium in 24 hours showed heavy saluresis: 593 mmol/day (40-220 mmol/day) According to the results of water deprivation test The patient was diagnosed as partial central diabetes insipidus Urine osmolality 302 mOsm/kg, after desmopressin admistration 699 mOsm/kg The patient started treatment with oral desmopressin 0.2 mg/day

Outcome and follow up: The polyuria did not improve despite increasing doses of desmopressin. Even though the patient did not complain of palpitation, he was referred to cardiac electrophysiological studies for his persistent PVCs. Holter showed episodes of sinus tachycardia, frequent polymorphic PVCs (16%) with numerous couplets and triplets. Echo: dilated right and left ventricular internal dimensions with mildly reduced ejection fraction:41% Cardiac MRI: scattered left ventricular mural myocardial areas of altered bright signals on T2w with delayed myocardial enhancement Suggesting inflammatory myocarditis not ischemic disease. The polyuria improved on anti-arrhythmic drugs (b blockers) in addition to anti-ischemic measures.

Conclusion: Inhibition of ADH occurs in cases of atrial dilatation that leads to the diuresis response. Also, atrial distension leads to ANP release, which has powerful diuretic and natriuretic properties and usually associated with saluresis and can give false positive results with water deprivation test. We report a case of apparently healthy male presenting with polyuria as sole presentation of dilated cardiomyopathy misdiagnosed as diabetes insipidus (DI) by water deprivation test.