Successful Treatment of Poikilodermatous Mycosis Fungoides with 308-nm Excimer Laser

Mycosis fungoides (MF) encompasses a variety of subtypes, ranging from indolent to aggressive forms, and generally progresses slowly before advancing to the tumor stage [1]. Among them, poikilodermatous MF (PMF) is a rare clinical variant of patch-stage MF, which is characterized by cutaneous atrophy, mottled-reticular pigmentation, and telangiectasia [2‒4].

PMF typically has a favorable prognosis, comparable to that of conventional patch-stage MF [2‒4]. Here, we report a case of PMF successfully treated with a 308-nm excimer laser.

A 50-year-old woman visited our outpatient clinic with a 3-year history of pigmented macules on her left thigh. She had been treated with topical difluprednate ointment and maxacalcitol ointment; however, the pigmented lesion gradually spread. On her initial visit, a physical examination revealed atrophic, annular, patchy, and reticular pigmented macules with slight erythema on the posterior and lateral aspects of the left thigh (Fig. 1). A biopsy specimen showed vacuolar degeneration with individual keratinization of keratinocytes in the epidermis. Lymphocyte infiltration was predominantly observed in the papillary dermis and the perivascular area of the superficial dermis (Fig. 2a). Immunohistochemical staining revealed that the infiltrated lymphocytes in the epidermis were positive for CD2, CD3 (Fig. 2b), CD4 (Fig. 2c), and CD5, but negative for CD7 (Fig. 2d), CD8, CD10, CD20, CD79, Granzyme B, TIA-1, and EBER. There was no evidence of T-cell receptor (TCR) β chain gene rearrangement. Based on these findings, the patient was diagnosed with PMF. Treatment with a 308-nm excimer laser (1,250 mJ/cm², 5 fractions) combined with topical difluprednate ointment was initiated. After 3 months, the pigmented erythema improved, leaving only slight pigmentation (Fig. 3).

Poikiloderma is a descriptive term referring to a combination of cutaneous atrophy, telangiectasia, and macular pigmentary changes that result in a mottled skin appearance [5]. The differentiation of poikiloderma is diverse, and its differential diagnosis is crucial for the management of patients with PMF. For example, skin conditions with polymorphous skin atrophy, such as atopic dermatitis, lichen planus, amyloidosis, and systemic lupus erythematosus, should be differentiated from PMF [5]. Although PMF generally has a favorable prognosis, it is often misdiagnosed as other conditions, leading to delays in diagnosis [2‒4].

As with other subtypes of MF, the diagnosis of PMF depends on immunohistopathological findings, such as T cells lining the basement membrane, the absence of CD7 expression, and confirmation of TCR rearrangement [1, 5]. PMF is typically characterized by the development of large plaques, and its most common site of onset is the so-called holster sign area, which extends from the buttocks to the lower back [5]. In our case, the clinical and histopathologic findings were consistent with PMF, despite the absence of detectable TCR β-chain rearrangements. Notably, the Southern blotting and PCR have limitations in detecting clonality, especially in early stage MF, as previous report suggested [6, 7]. In addition, the T-cell clonality positivity was not always detected in PMF [8]. From the above the point of views, one possible explanation is that TCR rearrangements can be challenging to detect in cases with low cell density, as seen in our present case.

For the treatment of PMF, the effectiveness of phototherapy, such as psoralen ultraviolet (UV) A and narrowband ultraviolet B (NB-UVB) [2, 3], and radiotherapy [4] has been reported. Notably, the 308-nm excimer laser emits high-energy monochromatic light with a wavelength close to the NB-UVB peak [6]. In dermatology, the excimer laser has been used for the treatment of vitiligo, psoriasis, alopecia areata, and MF in early stage [9‒13]. Since the energy level of the excimer laser is higher than that of conventional UV therapy [10], and because UV therapy is recommended for the patch stage of MF [14], the excimer laser is expected to be more effective than conventional UV therapy. In fact, in our case, only five sessions of excimer laser treatment significantly improved the infiltrated erythematous area, leaving only slight pigmentation. Although no clinical trials have been conducted to confirm the exact efficacy of the excimer laser in treating PMF, and although the effects of topical steroids should also be considered despite topical steroids were not useful as a monotherapy, our case suggests the potential of excimer laser as an effective therapeutic option for PMF.

It should be noted that, unlike inflammatory skin diseases, tumor immunity plays a significant role in the treatment of MF [15]. Therefore, dermatologists should exercise caution when using the excimer laser in advanced stages of MF, particularly after the tumor stage. In general, PMF has a better prognosis compared to other forms of MF, and excimer laser treatment may be recommended for PMF [11‒13], as most cases are diagnosed in the early stage. While this report describes only a single case, additional cases could provide fundamental insights into the therapeutic effects of excimer laser treatment for PMF.

Written informed consent was obtained from the patient for publication of the details of her medical case and any accompanying images. The protocol for this human study was approved by the Ethics Committee of Tohoku University Graduate School of Medicine, Sendai, Japan (permit No. 2021-1-1213).

The authors have no conflicting interests to declare.

There is no funding source to declare for this study.

All authors were involved in the treatment of the patient and the acquisition of clinical data. Manami Watanabe and Taku Fujimura drafted the manuscript. Yoshihide Asano supervised the study.

All data generated or analyzed during this study are included in this article. See also online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000544164). Further inquiries can be directed to the corresponding author.