Folliculotropic Mycosis Fungoides in a Teenager Treated With re‐ <scp>PUVA</scp> and Photodynamic Therapy

A 15-year-old male with no relevant medical history presented to our dermatology department with a three-year asymptomatic dermatosis initially involving the frontal and perioral regions, trunk, and limbs. Two previous skin biopsies had shown a slightly spongiotic reaction pattern with infundibular hyperkeratosis and a perifollicular inflammatory infiltrate. Multiple courses of topical and systemic corticosteroids, as well as topical and oral retinoids (isotretinoin 10 mg/day), were ineffective. Physical examination revealed infiltrated plaques with multiple milia cysts and comedone-like lesions on the frontal and perioral regions, along with partial eyebrow alopecia (Figure 1A,B). The trunk and limbs presented multiple well-demarcated erythematous and hypopigmented plaques with follicular hyperkeratosis, rough surface, and areas of localized alopecia. Laboratory and serological investigations were unremarkable. Histology of a facial lesion showed follicular ectasia with keratin plugs and a moderate dermal infiltrate with interstitial and periadnexal distribution, composed mainly of small to intermediate lymphocytes with irregular nuclei, demonstrating folliculotropism (Figure 1C). Immunohistochemistry demonstrated CD2, CD3, CD4, and CD5 positivity, low CD8 expression, and absence of CD20 and CD7. Molecular analysis confirmed T-cell clonality of the T-cell receptor beta chain gene. Thoraco-abdominopelvic computed tomography (CT) excluded systemic involvement. A diagnosis of folliculotropic mycosis fungoides (F-MF), stage IB, was established. Treatment with acitretin (20 mg/day) and oral psoralen plus UVA phototherapy (re-PUVA) was initiated. After 4 months of re-PUVA, there was near-complete clearance of the trunk and limb lesions and partial eyebrow regrowth, although infiltrated plaques with milia cysts and comedo-like lesions persisted on the frontal and perioral areas. Given their refractory nature, photodynamic therapy (PDT) targeting the facial lesions was initiated at month 4 alongside re-PUVA. A 16% methyl-aminolevulinate cream (Metvix) was applied under occlusion for 3 h, followed by red light irradiation for 12 min (630 nm, 37 J/cm2; Aktilite). Adverse effects were limited to moderate pain during illumination and transient erythema and edema within the first week, without further complications. At Month 9, after continued re-PUVA and four bimonthly PDT sessions, complete clinical response was achieved, with marked improvement of facial lesions and full eyebrow regrowth (Figure 2A,B). Complete clinical response persisted at the three-month follow-up; however, longer follow-up is required. Mycosis fungoides (MF) is the most common cutaneous T-cell lymphoma, but pediatric patients account for fewer than 5% of cases [1]. Folliculotropic MF (F-MF) is a distinct subtype with specific clinical, histopathological, and therapeutic characteristics [2]. In pediatric populations, F-MF is reported as the second most common MF subtype after the hypopigmented type [2]. Although the prognosis of early-stage F-MF appears similar to conventional early-stage MF, F-MF is more resistant to skin-directed therapies [2]. Therapeutic evidence in children remains limited, with management largely extrapolated from adult studies [3]. Phototherapy is a cornerstone of pediatric MF treatment, with narrowband UVB being the most frequently used modality for early-stage disease. Oral psoralen–UVA is typically reserved for thicker plaques or F-MF [3]. Photodynamic therapy has recently gained attention as a targeted, non-invasive treatment for MF, with encouraging results [4, 5]. A systematic review of PDT for relapsed or refractory MF reported a 63.2% complete response rate across 117 lesions, particularly with repeated sessions and long-wavelength light sources [4]. A prospective study in 12 patients with early-stage MF treated with monthly methyl-aminolevulinate PDT for 6 months revealed a response in 75% of patients, with better outcomes in sun-protected areas [5]. PDT offers several advantages—excellent cosmetic outcomes, noninvasiveness, high selectivity, minimal cumulative toxicity, negligible systemic photosensitivity, and low carcinogenic risk—supporting its use in localized relapsed or refractory MF, including F-MF, even in cosmetically sensitive areas [4, 5]. This case highlights the successful use of PDT as adjunctive therapy in a pediatric patient with F-MF resistant to conventional treatment. The authors have nothing to report. This material is the authors' own original work, which has not been previously published elsewhere. The patients in this manuscript have given written informed consent to the publication of their case details. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.