(36) Cutaneous Mastocytosis Presenting as Isolated Unilateral Labial Swelling

Background: Cutaneous mastocytosis (CM) is a rare disorder of pathologic accumulation of mast cells in the skin. It typically presents as multiple yellow-brown papules or plaques, or, less commonly, nodular lesions on the trunk, extremities, or scalp. Cutaneous symptoms include erythema, flushing, localized urticaria, swelling, dermatographism, or blister formation. Other symptoms include nausea, vomiting or diarrhea. Systemic symptoms can be triggered by temperature changes, exercise, hot baths, emotional stress, or certain medications. Darier’s sign is a diagnostic maneuver where manual friction is applied to the lesion as a trigger. While several cases of vulvar mastocytomas have been reported, to date, only three had labial swelling as their main presentation.

Case: A 4-year-old female presents with a 1.5-year history of facial flushing after physical exertion followed by 2-3 days of non-pruritic left labial swelling. Her left labia measured 4-6 cm at baseline and swelled significantly during the episodes causing severe pain. These flares were sometimes associated with emesis and fatigue. No other lesions were noted on initial exam. Pelvic ultrasound showed ill-defined fibrous tissue with no fluid collections nor abnormal vasculature; the MRI was normal. Her itching was mildly responsive to diphenhydramine and warm baths, but not to topical triamcinolone ointment.

Given the persistent symptoms, surgical excision was performed. Pathology was consistent with a mastocytoma. Follow up labs revealed a normal CBC/differential, CMP, and tryptase. The family was educated on CM triggers, and the patient was started on levocetirizine 2.5 mg daily. On follow up exam, she was noted to a yellow-brown thin papule on paraspinal back with a positive Darier sign and dermatographism. At her 1-year follow-up, her new flares started causing asymmetrical swelling involving her right labia with subcutaneous nodularity, and yellow papules and plaques at her posterior fourchette and right labia. Due to noted expansion of her disease, her regimen was updated to levocetrizine 2.5 mg twice daily with hydroxyzine as needed for flares instead of diphenhydramine due to new history of paradoxical reactions.

Comments: This is a unique case of CM presenting with left labial swelling, instead of papules, plaques, or nodules, triggered by physical exertion. This case and the other three with labial swelling show the importance of adding CM to the differential for isolated labial enlargement. Additionally, unlike the other cases, she did not initially have any other typical skin findings until later into her disease process.