Blistering Langerhans cell histiocytosis: LANCET case report
A previously healthy 6-month-old male infant was brought to an external dermatology clinic with an eruption of non-tender and non-pruritic vesicles and blisters over his truncal region that had appeared within the previous month.

He was subsequently referred for evaluation and investigations. The patient had no preceding or intercurrent illness, nor any positive contact or travel history. His only notable family history was atopic dermatitis in his mother and brother.

On physical examination, there were several small vesicles and large blisters filled with clear fluid distributed over the back and gluteal region. Some of the vesicles and blisters had resolved spontaneously, with residual scaly erythematous plaques and papules. The face and extremities were not involved.

A punch biopsy over the residual plaques showed a mixed inflammatory infiltrate in the superficial dermis consisting primarily of large histiocytic cells with kidney-shaped nuclei and abundant light pinkish cytoplasm. These cells were also seen in small vacuoles in all levels of the epidermis, and stained positively for CD1a, S100, and Langerin (CD207) immunohistochemical stains.

The BRAFV600E immunohistochemical stain was positive, indicating a mutation in the gene. Admixed eosinophils and lymphocytes were present within the dermal infiltrate. A diagnosis of Langerhans cell histiocytosis was made on clinical-pathological correlation.

A full blood count, skeletal survey, ultrasound of the hepatobiliary system, liver function test, and microscopic urinalysis did not reveal any extra-cutaneous manifestations of Langerhans cell histiocytosis. Treatment was started with mometasone furoate 0·1% topical cream twice daily. After 3 months, there was significant clinical improvement and resolution of the lesions.

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