Diffuse cutaneous mastocytosis (DCM) is a rare and severe form of cutaneous mastocytosis which may present in the neonatal period; thus early recognition is essential. Symptoms of mastocytosis are exacerbated by mast cell degranulating agents more commonly from heat, friction, local trauma, drugs and food. This is a case of DCM presenting with bullous eruptions after immunization.

An 11-month-old boy presented with generalized erythematous to hyperpigmented macules and patches initially at birth, with progression to bullous eruptions immediately after immunization without any systemic symptoms. Biopsy revealed superficial and deep mixed cell infiltrates consisting of lymphocytes, histiocytes and numerous mast cells. Giemsa stain highlighted the metachromatic mast cell granules. Serum tryptase was elevated by 13 times (130 ug/L). The patient was prescribed oral antihistamines and topical steroids that offered good response. Avoidance of all potential triggers was instructed.

The extensive cutaneous involvement in DCM (generalized erythema, diffuse papules that develop pachyderma, darker skin, peau d’orange) are due to the diffuse infiltration of the dermis with mast cells, accompanied with an elevated serum tryptase.

Unique to this local case are exacerbations triggered by vaccination. There is literature to support evidence of vaccination reactions to pentavalent vaccine in children with DCM though the pathway associated with mast cell degranulation after immunization has not yet been specified.

It is advised that patients with DCM follow scheduled immunization guidelines with precautionary measures.