Congenital cutaneous mastocytosis mistaken for non-accidental injury.

A previously well male infant presented to his general practitioner (GP) for his routine 6-week check. His parents reported the presence of tan-brown lesions since birth. The marks were uniform in color, were present on the trunk, scalp, and face, and were not overlying bony prominences. The GP was concerned that these lesions represented bruising as a manifestation of non-accidental injury (NAI), and arranged an urgent review at our pediatric department. Following assessment by the pediatric team he was admitted for investigation of potential NAI, and dermatology consultation was sought. On examination, scattered reddish brown to tan macules and papules were noted on the torso and limbs, not overlying bony prominences (Figure 1A, B). Darier’s sign was negative, although some reactive cutis marmorata was appreciable on the trunk following the rubbing of multiple lesions. A diagnosis of urticaria pigmentosa (UP), now known as maculopapular cutaneous mastocytosis (CM), a form of CM, was made clinically. Skin biopsies demonstrated an infiltrate of spindled and round mast cells and scattered eosinophils within the superficial and mid dermis, with immunohistochemistry positive for CD117, consistent with CM (Figure 1C–E). Blood tests during admission showed a normal complete blood count and coagulation screen (including von Willebrand factor), normal renal and liver function, normal lactate dehydrogenase, normal immunoglobulins, and normal mast cell tryptase. Cranial ultrasound and abdominal ultrasound (including liver and spleen) were normal.