DISCUSSION
MF is the most common type of cutaneous T cell lymphoma accounting for 50% of all primary cutaneous lymphomas 4,5. MF includes several variants based on the clinical and immunohistological characteristics 1 32. Some clinical variants of MF such as bullous MF and hyperpigmented MF or hypopigmented MF have clinical behavior similar to that of the classic MF. Accordingly, they are not considered separately. In contrast, some variants of MF such as F-MF, pagetoid reticulosis, and granulomatous slack skin have distinctive clinicopathologic features and therefore are considered distinct entities 4,5,29,32.
F-MF is a very aggressive subtype of MF and usually, the patients need aggressive interventions in contrast to classic MF 29. Gender distribution in F-MF shows a male-to-female ratio of 3:1 and a mean age of 55 years at the time of presentation. F-MF is very rare in adolescents and children with few cases being reported in the literature to date 20,30.
The clinical features of the case reported here concur with the previous studies 14,27-29. Bonta et al reported a case of a 44-year-old male patient with a generalized pruritic eczematous eruption. The patient developed an aggressive, rapidly progressive F-MF involving the scalp, eyebrows, and axillae. This was associated with follicular mucinosis, alopecia, and lymphomatous involvement of the inguinal lymph node. Histological examination of the skin biopsy revealed follicular mucinosis, folliculotropism of atypical cells, and intrafollicular Pautrier’s microabscesses 14.
The histological differential diagnoses in the case presented here revolved around follicular lymphomatoid papulosis, follicular eczema, and pseudolymphomatous folliculitis 18,33. Follicular lymphomatoid papulosis (LyP) is characterized clinically by a “waxing and waning” of the skin lesions and histologically by the presence of eosinophils and expression of CD30 protein 18,33. Follicular eczema is characterized by prominent spongiosis of the interfollicular epidermis and the lack of lymphocyte atypia. Pseudolymphomatous folliculitis that can be drug-induced is separated from F-MF by the presence of lymphoid follicles with germinal centers, and folliculotropic infiltrate is composed predominantly of CD3 positive cells admixed with CD20-positive, S100-positive, and CD1a-positive cells17. Some authorities in Dermatopathology (Gerami and Guitart, and Mitteldorf) proposed the presence of five histomorphologic patterns for F-MF including the “Prototypic” pattern with intact hair follicles, folliculotropism with or without follicular mucinosis, eosinophilic folliculitis, basaloid folliculolymphoid hyperplasia with folliculotropism, granulomatous dermatitis associated with follicular destruction, and follicular cysts with folliculotropism17,24. In agreement with other studies, we found the deposition of mucin in the follicular epithelium. Mucin deposition represents a response of the host follicular epithelium to injurious agents and can be encountered in several conditions such as follicular eczema, granulomatous rosacea, Ofuji’s disease, contact dermatitis, F-MF, angiolymphoid hyperplasia with eosinophilia. Taken together, these pathological conditions were lumped under the terminology of ”Alopecia mucinosa or Follicular mucinosis”. Some authorities consider follicular mucinosis as an ”abortive cutaneous lymphoma” 4,529.
To sum up, F-MF is a rare and under-recognized variant of MF. Its salient clinicopathologic findings include frequent head and neck involvement, folliculotropism, nuclear atypia, and mucin deposition in the follicular epithelium. The prognosis of FTMF is poor compared to classical MF. The early disease has 10 years survival of 82% and 42% by 15 years. The late disease has a similar prognosis as classical MF (91% at both 5 and 10 years) 30The diagnosis of F-MF requires a high index of suspicion both on the part of the dermatologist and dermatopathologists.