A 59-year-old Caucasian heterosexual man presented with malaise and dizziness. General examination revealed no peripheral oedema, no clubbing or lymphadenopathy and systemic examination was otherwise normal. His initial investigations showed hyponatremia with serum sodium 121 mmol/l, potassium 3.4 mmol/, serum osmolality 255 mOsml/kg, and urine osmolality 672 mOsml/kg. The rest of blood tests including; thyroid function, short Synacthen test, full blood count, liver functions, urea and creatinine were all normal chest X-ray showed consolidation at the left base. He was treated for pneumonia with secondary SIADH.
He returned 1 month later with anorexia, weight loss, night sweats and unsteadiness, with a sodium of 122 mmol/l. He underwent CT thorax and abdomen which revealed 5 mm pulmonary nodule. His case was discussed in the chest multidisciplinary team meeting with a decision to monitor this nodule with interval CT scanning to exclude an underlying neoplasm or TB. Tumour markers were normal and sodium improved with demeclocycline.
Several months later repeat CT showed the pulmonary nodule had increased to 6 mm with hilar and abdominal lymphadenopathy. He was referred to the tertiary centre where the nodule was excised and found to be benign.
He was admitted later with fever, night sweats and weight loss. He had oral candidiasis. An HIV test was carried out and reported positive. Subsequently he was found to have pneumocystic jiroveci, syphilis, cytomegalovirus (serologically), B-cell lymphoma, HIV encephalopathy and he was transferred to the infectious diseases unit for treatment.
Hyponatraemia can be associated with HIV for multiple reasons including SIADH (secondary to pulmonary and CNS infections or malignancy), adrenal insufficiency (usually infective involvement of the adrenal glands), HIV enteropathy, HIV-associated nephropathy or direct infection of the posterior pituitary (CMV).