Sunrise Teaching 19/11/15 Elaine McKinley

Clinical Scenario 5 yr old with polydipsia/polyuria and dilute urine/no glucosuria.

Diabetes Insipidus (DI) Inappropriate passage of large volumes of dilute urine (<300mOsm/L). Due to either deficiency in ADH* (anti-diuretic hormone) production [cranial DI] or resistance to its actions at the kidney [nephrogenic DI]. *Also known as arginine vasopressin (AVP)

Epidemiology The combined prevalence of cranial DI and nephrogenic DI combined is estimated at 1 in 25,000. Inherited causes account for approximately 1-2% of all cases of DI.

Cranial DI Acquired: Idiopathic Tumours Intracranial surgery Head injury Infections Vascular Post-radiotherapy Inherited: Autosomal recessive combination of DI, diabetes mellitus, optic atrophy, deafness (DIDMOAD) - Wolfram syndrome Autosomal dominant mutations of vasopressin gene

Nephrogenic DI Acquired: Idiopathic. Hypokalaemia Hypercalcaemia Chronic kidney disease Drugs: eg, lithium Renal tubular acidosis Post-obstructive uropathy Inherited: X-linked mutation in V2 ADH-receptor gene Autosomal recessive defect in aquaporin 2 (AQP2) gene – water channel in distal renal tubule Sporadic nephrogenic DI with mental retardation and intracerebral calcification (exceedingly rare)

Gestational DI due to accelerated metabolism of ADH by placental production of cysteine aminopeptidases

History Polyuria Polydipsia Chronic thirst Nocturia Urinary incontinence Secondary nocturnal enuresis Loss of appetite Fatigue

History Young Children: Excessive, heavy wet nappies Excessive crying Irritability Failure to thrive/weight loss Hyperthermia

History PMHx/Family hx to assess for Risk Factors– Cranial DI: Recent CNS infection, Pituitary surgery, craniopharyngioma, pituitary stalk lesions, traumatic head injury, congenital pituitary malformations, genetic mutations (Wolfram's syndrome), AVP-neurophysin gene mutations, and autoimmune disorders Nephrogenic DI: Use of lithium and AVP receptor pathway mutations

General Examination Observations: Tachycardia Hypotension Hyperthermia Assess hydration status dry mucous membranes poor skin turgor ? shocked Rash Growth Parameters – ? thriving

Examination Presence of intercurrent illness Neurological examination – muscle twitching hyper-reflexia visual field defects focal motor deficits sensorineural deafness

Investigations

Differential Diagnosis Psychogenic or primary polydipsia Diabetes mellitus Other osmotic diureses - eg, hypercalcaemia Diuretic abuse

Primary polydipsia/Dipsogenic DI/ Psychogenic polydipsia Excessive/abnormal thirst, accompanied by intake of excessive quantities of water or fluid. Often seen in patients with severe mental illness and/or developmental disability. There may be no physical effects, but hyponatraemia can occur. Diagnosis of exclusion.

Management Rehydration Treat underlying cause Desmopressin if Cranial DI Consider Sodium Restriction