Background Cutaneous mastocytosis (CM) is a disease characterised by abnormal proliferation of mast cells in the skin causing pruritic rashes over the body, mainly in infants and small children. The authors report an infant with non-pigmented plaque forming CM, who was treated for 18 months as atopic dermatitis, which it mimicked until a biopsy was done.
Case Report This 9 months old Caucasian male infant had a persistent, intensely pruritic rash from the age of 6 weeks. He was also “developing white lumps wherever touched”, as well as intermittent blisters. There was strong family history of atopy. Differential diagnosis of cow's milk intolerance was considered and the feed was changed to soya milk, and later to Neocate, with no improvement. Milk-free weaning was also discussed. Child developed diarrhoea while on Neocate. Examination revealed a thriving infant with extensive erythematous plaquey lesions over the trunk and extremities that urticated on touch (figure 1). Darier's sign (weal and surrounding erythema developing after stroking the affected skin) was demonstrated (figure 2). Investigation showed low levels of neutrophils, low IgG and normal inflammatory markers and functional antibodies. Radioallergosorbent test to milk and egg was negative. A skin biopsy later confirmed CM.
Discussion CM is a condition with mast cell proliferation and accumulation in the skin. Urticaria pigmentosa is the most common variety in children, followed by solitary mastocytoma. However, non-pigmented plaque forming lesions can occur in infancy and are often missed. Stem cell factor, a cytokine produced by many tissues, plays a key role in stimulating CD34 cells expressing KIT protein to transform to mastocytes (figure 3). Systemic symptoms including headache, flushing, dizziness, syncope, diarrhoea, etc, can occur following mast cell degranulation by exposure to heat, cold, sunlight, friction or certain medications.
Conclusion Lack of awareness about this uncommon condition may lead to delayed diagnosis causing frustration in parents. Darier's sign (elicited by stroking the lesion causing urticarial weal within the lesions) is a simple clinical sign that helps to clinch the diagnosis, avoiding unnecessary investigation and inappropriate treatment.