Pediatric Mycosis Fungoides and Hydroa Vacciniforme Lymphoproliferative Disorder.

Patients most often present with hypopigmented patches, though folliculotropic disease is also common. Prognosis is usually excellent. Most patients are diagnosed with early-stage disease, and less than 5% of cases progress to late-stage disease. Pediatric MF can be difficult to recognize. It often mimics more common benign inflammatory and pigmentary dermatoses. Furthermore, clinicians may be hesitant to perform skin biopsies in younger patients, contributing to delays in diagnosis. Evaluation and treatment guidelines largely follow those of adult MF, with special considerations regarding age and expected lifetime exposure to therapy. Adaptations include limiting unnecessary ionizing radiation, relying more heavily on ultrasound as an imaging modality, and balancing disease control with the long-term safety of treatments, including topical corticosteroids and mutagenic therapies such as PUVA, mechlorethamine gel, and radiation. Despite favorable outcomes, the chronic nature of MF can lead to substantial psychosocial burden on both the patients and their families. Caregivers must navigate frequent visits, uncertainty about recurrence, and concerns about long-term adverse effects. Management should therefore incorporate developmentally appropriate communication, psychosocial support, and long-term follow-up. This chapter reviews the epidemiology, clinical and pathologic features, diagnostic approach, staging, and treatment of pediatric MF. It highlights the distinctions between pediatric and adult disease, recently developed recommendations, and the importance of individualized, family-centered care. Because the clinician evaluating a child with an atypical or persistent eruption must distinguish pediatric MF from other rare cutaneous lymphoproliferative disorders, this review also discusses hydroa vacciniforme lymphoproliferative disorder (HV-LPD). Although HV-LPD is a distinct Epstein-Barr virus--associated entity rather than a variant of MF, it is included here because it is one of the few primary cutaneous lymphoproliferative disorders of childhood. It therefore shares the diagnostic challenges of mimicking benign dermatoses and requiring careful clinicopathologic and immunophenotypic correlation, and represents an important consideration in the pediatric differential diagnosis.