BMJ Case Reports 2018; doi:10.1136/bcr-2017-222916
  • Findings that shed new light on the possible pathogenesis of a disease or an adverse effect

Considering exercise-associated hyponatraemia as a continuum

  1. Tamara Hew-Butler3
  1. 1Family and Community Medicine, Via Christi Health System, Wichita, Kansas, USA
  2. 2Precision Hydration, Christchurch, UK
  3. 3Exercise Science, Oakland University, Rochester, Michigan, USA
  1. Correspondence to Dr Tamara Hew-Butler, hew{at}
  • Accepted 17 February 2018
  • Published 9 March 2018


Exercise-associated hyponatraemia (EAH) always involves a component of overhydration relative to available exchangeable sodium stores. In the majority of cases, this is purely due to excessive consumption of fluids during exercise. In a lesser number of cases, it is apparent that excessive sodium loss through sweat may play a role by decreasing the amount of acutely available exchangeable sodium. Two cases demonstrating the latter, one in an individual with cystic fibrosis (CF) and another in an endurance athlete without CF, demonstrate how elevated dermal sweat losses may contribute to a relative dilutional EAH along a pathophysiological continuum.


  • Contributors All authors contributed to planning and design and editing. TH-B and DL have functioned as co-corresponding authors. DL produced the first draft of the manuscript. TH-B provided first draft of the tables/figures. AB and JT provided materials and equipment for pilocarpine testing. All authors were present for and participated in pilocarpine testing.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests Not required.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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