Rhabdomyolysis and hyponatremia: a cluster of five cases at the 161-km 2009 Western States Endurance Run.

OBJECTIVE: Five of 400 starters of the 2009 Western States Endurance Run (WSER) were hospitalized with hyponatremia and rhabdomyolysis. This article explores the risk factors associated with development of hyponatremia and rhabdomyolysis.
METHODS: Data on the 5 cases were collected retrospectively from the runners and medical records, and all race participants were invited to complete a post-race survey. Characteristics of the cases were compared with the other race participants.
RESULTS: The 5 runners developing hyponatremia with rhabdomyolysis were men with a mean (±SD) age of 39 ± 7 years. Presenting complaints included neurological symptoms among 3 and nausea among 3. Compared with those runners not developing hyponatremia with rhabdomyolysis, the cases tended to be younger, faster, more likely to have sustained an injury which interfered with training prior to the race, and were more likely to use nonsteroidal anti-inflammatory drugs (NSAIDs) during the race. The 3 of 5 cases progressing to acute renal failure were characterized by higher initial blood urea nitrogen (BUN; 43-69 vs 18-23 mg/dL) and creatinine (2.8-4.9 vs 1.1-1.2 mg/dL) levels but were not distinguished by creatinine phosphokinase (CPK) concentrations.
CONCLUSIONS: Over 1% of participants in the 2009 WSER were hospitalized with hyponatremia in combination with rhabdomyolysis. These individuals tended to be younger, faster, more likely to have had an injury that interfered with training, and more likely to have used NSAIDs during the race. Higher initial BUN and creatinine levels, but not CPK concentrations, distinguished those 3 who progressed to acute renal failure.