Urticaria pigmentosa---change in conscious state associated with rise in plasma histamine levels.

The case is described of a 42-year-old man with urticaria pigmentosa and documented systemic mastocytosis who had 2 episodes of loss of consciousness, headache, nasal stuffiness and faecal incontinence, following a swim in a river. Under controlled conditions the patient was subjected to immersion of the right hand to icewater for a period of 2 minutes, followed by 2 minutes of strenuous exercise. Similar symptoms involving change in conscious state were evoked with accompanying rises in plasma histamine levels. These findings suggest that histamine is at least one of the major mediators of the change in conscious state that is reported rarely in these patients and draws attention to the neurological facets of this rate disorder.