Background: Diabetes insipidus, now called arginine vasopressin deficiency, is an uncommon endocrine disorder characterized by abnormality in antidiuretic hormone (ADH). It is either due to insufficiency in ADH or decreased peripheral response to normal levels of ADH. It commonly manifest as polyuria and polydipsia. There have been very few cases reported in medical literature highlighting the correlation between untreated common variable immunodeficiency (CVID) and arginine vasopressin deficiency (AVPD). Here we present a case of AVP-D in patient with established but untreated CVID

Case description: A male in his mid-fifties presented with altered mental status and was found to have sepsis secondary to community acquired pneumonia. Additionally, he complained of significant thirst and large amounts urine output which has been ongoing for four months but was not adequately addressed. His urine output was noted to be 7.2 Liters in 24 hours with an inappropriately low urine osmolality in the setting of hypernatremia as documented below. This raised the suspicion for ADH imbalance which led us to pursue water deprivation test. It revealed minimal change in urine output and osmolality. This further led us to perform a desmopressin challenge test. We administered 4 mcg of desmopressin (DDAVP) subcutaneously which resulted in an appropriate decrease in urine output in addition to increase in urine osmolality (A Delta of 40 mOsm/kg representing >50% increase in urine osmolality). This was consistent with central AVPD. He was started on DDAVP and immunoglobulin replacement therapy.

Discussion: CVID is a hereditary hypogammaglobulinemia with reported 20% of patients with concomitant autoimmune endocrine disorders. Untreated CVID leads to the involvement of multiple organ systems, as was the case with our patient who had features of CVID enteropathy, CVID granulomatous Interstitial lung disease, and now ADH imbalance emphasizing the condition's diverse manifestation. This correlation is poorly understood but is hypothesized to be linked to lymphocytic neurohypophysitis. Hence more in-depth research needs to be done into ADH imbalance in patients with CVID particularly if untreated. This case underscores the necessity of maintaining a high suspicion for AVP-D in patients with CVID to prevent debilitating yet reversible complications. Early recognition and appropriate replacement therapy are essential in improving patient outcomes and quality of life.