Recurrent mast cell degranulation causing episodes of hives, diarrhoea, swelling, dizziness, even anaphylaxis.

Thought to be due to clonal expansion of abnormal mast cells, not requiring usual triggers.

Diagnosis is on basis of rise in tryptase levels during an episode from base line. If base line tryptase is normal, then likely mastocytosis. Urine mast cell products eg leukotriene, prostaglandin? Look for KIT D816V on flow cytometry. Bone marrow aspiration?

Scoring systems available.

Treatment is predictably:

• Antihistamines, preferably non sedating. Some people however benefit from the additional sedative effect of older antihistamines eg ketotifen, hydroxyzine.
• Adrenaline autoinjectors for anaphylaxis self management
• Montelukast/zafirlukast has systemic anti-inflammatory action
• Famotidine has anti-histamine action
• Steroids for short term use
• Omalizumab