A 28-year-old woman recently completed her first marathon in 4 hours and 20 minutes. At the finish line, she complains of nausea. Soon thereafter, she starts having a headache and begins to vomit. She is taken to a nearby emergency department. She denies any past medical history.
Her temperature is 37.2 C (99 F), blood pressure is 125/72 mm Hg, and pulse is 84/min. Her mucous membranes appear moist. She is disoriented to time. She experiences a generalized tonic-clonic seizure soon after arrival.
Which of the following is the most likely diagnosis?

Question

A 28-year-old woman recently completed her first marathon in 4 hours and 20 minutes.  At the finish line, she complains of nausea.  Soon thereafter, she starts having a headache and begins to vomit.  She is taken to a nearby emergency department.  She denies any past medical history.
Her temperature is 37.2 C (99 F), blood pressure is 125/72 mm Hg, and pulse is 84/min.  Her mucous membranes appear moist.  She is disoriented to time.  She experiences a generalized tonic-clonic seizure soon after arrival.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient's presentation is consistent with acute cerebral edema due to exercise-associated hyponatremia (EAH). Hyponatremia is usually mild and asymptomatic after endurance events (e.g., marathons and triathlons). Excessive intake of hypotonic fluids during the event combined with non-osmotic release of vasopressin results in renal water retention and hyponatremia. Inexperienced female athletes are most susceptible to EAH. Patients with sodium levels of 128-134 mEq/L are usually asymptomatic or experience mild symptoms (e.g., nausea +/- vomiting, weakness, dizziness, bloating, and headache). As the sodium level further decreases, patients can develop cerebral edema, seizures, confusion, coma, and death. Diagnosis of EAH should be confirmed with serum sodium measurement before initiating empiric treatment. Current guidelines recommend fluid restriction in patients with mild symptoms and hypertonic saline for severe symptoms. Drinking only when thirsty (rather than at arbitrary times) can prevent EAH. In contrast to EAH, the "collapsed" athlete usually presents with hypernatremia (rather than hyponatremia) due to not drinking enough fluids. (Choice A) Cerebellar stroke usually presents in older patients with gait abnormalities, dizziness, headache, and sometimes limb coordination defects. (Choice B) Heat stroke results in palpable warmth and usually presents with elevated core body temperature, which is not seen in this patient. (Choice D) Some degree of rhabdomyolysis is often present after an endurance event. Significant rhabdomyolysis is usually associated with musculoskeletal complaints, oliguria, and dark urine. (Choice E) Volume depletion typically presents with hypotension, dizziness, and tachycardia. This patient's stable vital signs and moist mucous membranes make this diagnosis unlikely. Educational objective: Hyponatremia is commonly seen after endurance athletic events and is due to ingestion of large amounts of hypotonic fluids during the event. Hyponatremia is usually asymptomatic, but severe levels can result in nausea, vomiting, headache, disorientation, and seizures. __________ References: Hyponatremia among runners in the Boston Marathon. (http://www.ncbi.nlm.nih.gov/pubmed/15829535) Three independent biological mechanisms cause exercise associated hyponatremia; evidence from 2,135 weighed competitive athletic performances. (http://www.ncbi.nlm.nih.gov/pubmed/16344476)

A 28-Year-Old Woman Recently Completed Her First Marathon in 4