Pneumomediastinum and hyponatraemic dehydration as presenting features of cystic fibrosis.

Newborn screening for cystic fibrosis promotes early diagnosis and treatment, leading to a reduction in the number of late diagnoses [1]. This is of benefit to patients but contributes to physicians being less aware of the diverse ways in which unscreened patients present. We report a 12-year-old male who presented with pneumomediastinum and hyponatraemic dehydration, in whom subsequent investigations diagnosed cystic fibrosis. Hyponatraemic dehydration is well documented as a presenting feature of cystic fibrosis but usually occurs during periods of hot weather or after strenuous exercise [2]; neither was present in this case. Although pneumomediastinum is not uncommon in adults with advanced cystic fibrosis [3], it is very rare in children and has not previously been reported in combination with hyponatraemic dehydration.