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Education And Debate

Lesson of the Week: Cystic fibrosis presenting as hyponatraemic heat exhaustion

BMJ 1995; 310 doi: (Published 04 March 1995) Cite this as: BMJ 1995;310:579
  1. H R Smith, senior house officer in medicinea,
  2. G S Dhatt, consultant chemical pathologista,
  3. W M A Melia, consultant physiciana,
  4. J G Dickinson, consultant physicianb
  1. a Queen Elizabeth Military Hospital, London SE18 4QH
  2. b Princess Mary Hospital, Akrotiri, Cyprus
  1. Correspondence to: Captain H R Smith, Officers Mess, Cambridge Military Hospital, Aldershot, Hampshire GU11 2AN.
  • Accepted 6 June 1994

Cystic fibrosis is the commonest autosomal recessive disorder in Europe. It can present late with atypical features.1 Mutations in a gene on chromosome 7 that regulates transmembrane conductance cause the disease.2 Seventy two per cent of patients with cystic fibrosis are homozygous or heterozygous for eight mutations of the gene.3 The primary defect is low permeability of cell membranes to chloride ions which affects fluid transport during secretion and absorption by epithelial cells.4 We report a case of late presentation of cystic fibrosis in a man with the (del)F508 and R117H mutations.

Case report

A 24 year old infantryman was referred after having collapsed twice with hyponatraemia in hot climates. He said that he sweated more than his colleagues in the heat and formed a crust of salt on his skin in hot climates. Before these episodes he had been generally well with no medical history.

In 1991 he was posted to Saudi Arabia, where he underwent heat acclimatisation, which culminated in running 4.8 km after two months. His water intake was greater than his colleagues' during the run. He collapsed …

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