Syndrome of inappropriate antidiuretic hormone associated with eosinophilic granulomatosis and polyangiitis.

A 62-year-old man presented with classic signs and symptoms of eosinophilic granulomatosis and polyangiitis (EGPA, also known as Churg-Strauss syndrome)-mononeuritis multiplex, palpable purpura, hypereosinophilia, positive P-ANCA (perinuclear anti-neutrophil cytoplasmic antibodies) developed diffuse alveolar haemorrhage. The patient had longstanding mild hyponatraemia, but developed moderate and symptomatic hyponatraemia characteristic of the syndrome of inappropriate antidiuretic hormone. The patient's serum sodium returned to his baseline- mildly hyponatraemic, after initiation of treatment targeted towards EGPA. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.