1 May 2012
A 10-month-old male infant presented with a widespread skin eruption predominantly over the upper medial thighs. Apart from mild eczema, past medical history was unremarkable. A diagnosis of urticaria was made and he was discharged.
Progressive worsening of the rash prompted representation 2 days later. Morphology of the skin eruption now included blistering, non-scaly, golden crusting and ‘target-like’ lesions over the knees and groin. Treatment was started with flucloxacillin and acyclovir. A full blood count examination was normal. No initial serum tryptase was requested. Swabs of the lesions were sent for bacterial culture and viral polymerase chain reaction, both of which were negative. Overnight, the rash progressed and he developed a fever with associated cough and mild conjunctival injection. There was no organomegaly. Concern over involvement of the oral mucosa and genitalia prompted referral to a specialist centre.
On arrival, he was alert and had a widespread polymorphic eruption (Fig. 1). Fluid-filled vesicles in an annular configuration were present in the axillae and groin. There were no necrotic areas and the mucous membranes were intact. There was no history of flushing, diarrhoea or wheeze. Repeat full blood count examination was normal. A skin biopsy was taken and showed a dense infiltrate of mast cells within the dermis consistent with a diagnosis of cutaneous mastocytosis (CM). Given the extent of the cutaneous lesions, treatment was started with oral prednisolone (1 mg/kg once daily) and antihistamine (cetirizine 2.5 mg/ once daily). The following day, there was marked improvement. On further questioning, mum revealed that the areas of ‘eczema’ appeared to blister easily and typically resolved leaving a brownish discoloration particularly on his trunk. He was discharged on a weaning dose of oral prednisolone to complete a 2-week course. On follow-up 5 months later, he had remained well with only occasional flares that responded to antihistamines.
CM is a spectrum of clinical disorders that result from tissue mast cell hyperplasia. The most common organ affected is the skin, and systemic involvement is rare in children. The majority of cases present in the first year of life.[2, 3] Findings include the presence of reddish-brown or pale, pruritic monomorphic papules, plaques or nodules symmetrically distributed on the body. The face, head, palms and soles are characteristically spared. Patients often demonstrate Darier's sign with lesions becoming itchy and raised within a few minutes of gentle rubbing. This finding is highly specific for mastocytosis.
The most common form, urticaria pigmentosa, is characterised by widespread distribution of tan macules with typical sparing of the palms, soles, face and scalp. The other variants that occur in children are less common and include mastocytoma that presents as a solitary erythematous nodule or plaque in early childhood and diffuse CM that often presents in neonates.
Diagnosis of CM is based on history, clinical features and when undertaken typical histological features of a dense infiltrate of mast cells within the dermis on skin biopsy. Other laboratory investigations are rarely helpful. Patients should be advised about the avoidance of potential triggers. These include the use of non-steroidal anti-inflammatory medications and opiates, in addition to physical stimuli such as friction. Although there are no controlled clinical trials, antihistamine medications remain the main therapeutic option. Topical corticosteroids may be of benefit during flares of CM but treatment with systemic corticosteroids remains controversial.[4, 5] Patients should be kept under review and be advised to report potential systemic symptoms related to histamine release (headaches, flushing, gastrointestinal upset or collapse).