Atypical presentation of Addison’s disease

Discussion To diagnose hyponatraemia, the first step is to confirm hypotonic hyponatraemia by serum osmolality, followed by assessment of the volume status and urine osmolality. Hypotension and decreased cardiac output cause an increase in secretion of antidiuretic hormone (ADH) from posterior pituitary to absorb more water, leading to further reduction in Na concentration. Learning points > In hyponatraemia, serum osmolality, urine osmolality and urine Na should be tested, then assess the volume status of the patient to identify the cause of hyponatraemia. > If the patient is not responding to fluid restriction, Addison's disease should be considered. > Tuberculosis is the most common cause of Addison's disease worldwide, although autoimmune causes are common in the UK.