Hyponatremia as an underdiagnosed postpartum headache emergency: a case report

Postpartum headache is a common emergency department complaint with a wide differential diagnosis. Distinguishing primary from secondary, more sinister, causes of headache is an important skill for the emergency physician. We present a case of a 31-year-old G1P1 woman who presented at five days postpartum with a 48-hour headache and an otherwise uncomplicated pregnancy. She had several precipitating postpartum risk factors, including use of hypotonic fluids in labour, oxytocin to augment labour, changes in food and drink patterns, and was mildly hypertensive. Urgent investigations in the emergency department found her to be severely hyponatremic (sodium: 121 mmol/L (normal: 136-144)) without evidence of preeclampsia. She was admitted to hospital to correct her electrolyte imbalance. This case highlights the importance of remaining vigilant in differentiating concerning causes of postpartum headache, as well as identifying key precipitants which may put women at risk for postpartum hyponatremia.