MDMA-associated hyponatremia

Electrolyte Disordersmedium

A previously healthy 27-year-old man is brought in after being found down in a nightclub bathroom. He was well earlier and had at least a few mixed drinks interspersed with glasses of water. BP is 145/88 mm Hg and temperature 38°C; he is confused and diaphoretic. Serum sodium 120 mEq/L, creatine kinase 4300 U/L, serum osmolality 265 mOsm/kg H₂O. Urine osmolality is 457 mOsm/kg H₂O and urine sodium 58 mg/dL. Which substance most likely explains his laboratory abnormalities?

  1. A.Phencyclidine (PCP)
  2. B.3,4-methylenedioxy-methamphetamine (MDMA)Correct
  3. C.Cocaine
  4. D.Ethyl alcohol

Explanation

The most likely cause is 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). This young man collapsed at a nightclub with confusion, diaphoresis, hyperthermia, hypertension, rhabdomyolysis (creatine kinase 4,300 U/L), and acute hypotonic hyponatremia (sodium 120 mEq/L, serum osmolality 265 mOsm/kg) with an inappropriately concentrated urine (457 mOsm/kg) and urine sodium that is not low. This is the characteristic MDMA syndrome. MDMA and its metabolites stimulate vasopressin release directly and through serotonergic pathways, causing inappropriate antidiuresis. At the same time, users are encouraged to drink water to avoid overheating while dancing, and hyperthermia with sweating adds to thirst. Ingesting large volumes of water while unable to excrete it causes acute hyponatremia, which can rapidly produce cerebral edema, seizures, and death; young women are particularly susceptible. Serotonergic and sympathomimetic effects also produce hyperthermia, diaphoresis, tachycardia, hypertension, and muscle injury. Because the hyponatremia developed within hours and he is symptomatic with confusion, it should be treated promptly with a 100- to 150-mL bolus of 3% saline, repeated as needed, with cooling and fluids for rhabdomyolysis guided by sodium monitoring. Cocaine causes sympathomimetic toxicity with hypertension, hyperthermia, agitation, and rhabdomyolysis, but it is not associated with antidiuretic hormone release or acute hyponatremia. Ethyl alcohol suppresses vasopressin and causes a water diuresis; it would produce dilute urine, not a urine osmolality of 457 mOsm/kg. Beer potomania causes hyponatremia over days from low solute intake, not acutely after a night out, and alcohol does not cause hyperthermia or rhabdomyolysis of this pattern. Phencyclidine causes agitation, violent behavior, nystagmus, hypertension, hyperthermia, and rhabdomyolysis, but it is not a recognized cause of inappropriate antidiuresis and acute hyponatremia.

Why each option

A.
Phencyclidine causes agitation, nystagmus, hyperthermia, and rhabdomyolysis, but it is not a recognized cause of inappropriate antidiuresis or acute hyponatremia.
B.
Correct. Hyperthermia, diaphoresis, rhabdomyolysis, and acute hyponatremia with urine osmolality 457 mOsm/kg after a nightclub with heavy water intake indicate MDMA-induced antidiuresis.
C.
Cocaine causes sympathomimetic hyperthermia and rhabdomyolysis but does not stimulate vasopressin release, so it would not explain acute hyponatremia with concentrated urine.
D.
Ethanol suppresses vasopressin and produces a dilute water diuresis, inconsistent with a urine osmolality of 457 mOsm/kg and acute hyponatremia.

Reference: Spasovski G, Eur J Endocrinol 2014 (clinical practice guideline on diagnosis and treatment of hyponatraemia); Henry JA, Lancet 1998 (low-dose MDMA induces vasopressin secretion)

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