Lessons of the month: Pyroglutamic acidosis: long-term paracetamol and a high anion gap.

An 84-year-old woman presented in extremis with confusion and Kussmaul respiration. She had a history of urosepsis, renal impairment and osteoarthrosis. The venous blood gas showed a marked metabolic acidosis with a high anion gap. Lactate and ketones were normal. Her medications included regular paracetamol via a dosette box. Lactic acidosis and ketoacidosis being excluded, it emerged that the most likely cause of a high anion-gap acidosis in the presence of chronic paracetamol therapy is pyroglutamic acidosis, caused by the build-up of an acidic intermediate in the gamma-glutamyl cycle, the function of which is to synthesise glutathione. Paracetamol was stopped and fluids administered; she recovered over 7 days and was sent home. The biochemical diagnosis was confirmed by a central laboratory after discharge. This case emphasises the importance of the anion gap in diagnosis, and one important danger of chronic paracetamol administration.