Endocrine Abstracts

History: We present the case of a 47-year-old man with heart failure (HF) and cranial diabetes insipidus (CDI) secondary to Langerhans-cell-histiocytosis. In the context of worsening HF with increasing shortness of breath and fluid retention, careful desmopressin dose reduction provided adequate aquaresis to restore euvolemia, obviating the need for usual diuretic treatments.

Investigations: Echocardiography and a cardiac MRI revealed a non-dilated but severely impaired left ventricle (ejection-fraction 35%). His right ventricle was impaired but non- dilated. Sodium, paired osmolarities were within reference range throughout follow-up.

Treatment: Careful reduction of desmopressin from maintenance dose of 200 mg thrice-daily to 200 mg twice-daily allowed for adequate aquaresis and resolution of worsening HF symptoms. Iatrogenic diuresis was not indicated. Desmopressin adjustment manoeuvres were adequate to restore euvolemia, with urine output averaging 2-2.5 litres. After resolution of HF symptoms, desmopressin was switched back to 200 mg thrice-daily. Maximum tolerated Losartan dose was 50 mg. Beta-blockade, mineralocorticoid-receptor or angiotensin-receptor- neprilysin inhibition were not tolerated. SGLT-2 inhibition has not been trialled yet.

Conclusions: The co-existence of CDI and HF presents both challenges and unique therapeutic opportunities. Desmopressin dose manoeuvres produced adequate aquaresis, leading to restoration of euvolemia and rapid symptomatic relief. Dizziness, polyuria, thirst limited tolerability of HF prognostication drugs. Close endocrinology and cardiology co-operation was key in avoiding admissions with decompensated HF. This case provides insights for novel drug development targets. Our patient has complete absence of V1a-receptor activity (absent endogenous vasopressin). V2-receptor activity is dose-dependent based on desmopressin manipulation. Inducing a similarly balanced V1a/V2-receptor activity state pharmacologically could translate to clinically meaningful aquaresis, obviating V1a-receptor induced deleterious vasoconstriction and cardiac remodelling. This could represent a novel HF treatment target, potentially more effective than selective V2- receptor antagonism (tolvaptan) associated with toxic V1a-receptor activation via rebound endogenous vasopressin release. Pecavaptan, a novel balanced oral V1a/V2-receptor antagonist is under development.