Positron emission tomography for staging and response assessment of mycosis fungoides in a child.

Sir,

We report our experience with positron emission tomography and computerized tomography scan (PET-CT) in mycosis fungoides (MF). A 12-year-old boy presented with pruritic erythematous rash over left shin for 2 years. He was initially treated outside our center with topical steroids and antibiotics with minimal improvement. On examination, he had multiple hypopigmented macules on the back and buttocks and a well-defined erythematous to violaceous 6 × 6 cm plaque over medial aspect of left leg [Figure 1a]. He had few soft cervical lymph nodes (LN) measuring 1 cm. Skin biopsy from a macule on the back was non-contributory. Biopsy from left leg plaque showed atypical lymphocytic infiltrate in lower and upper dermis, with epidermotropism [Figure 1b]; lymphocytes were CD3-positive and negative for CD20 and CD30. Thus, the findings suggested a diagnosis of MF. CT scan of chest and abdomen revealed only horseshoe kidney. Left cervical LN biopsy showed dermatopathic lymphadenitis. Peripheral blood smear and bone marrow biopsy were normal. A whole body 18Fluorodeoxyglucose (FDG) PET-CT scan showed localized increased FDG uptake in subcutaneous thickening along anteromedial aspect of left leg [Figure 1c]. He was treated with topical clobetasone and psoralen plus ultraviolet-A radiation to the shin plaque for 3 months, followed by narrow-band ultraviolet-B radiation for 3 sessions (0.25, 0.3, and 0.36 J/m2), which resulted in only a partial response. Hence, he was administered local radiotherapy at a dose of 36 Gy in 18 fractions over 3½ weeks. The lesion subsided clinically except for residual hyperpigmentation [Figure 1d]. PET-CT done 10 weeks after completion of radiotherapy showed complete resolution [Figure 1e]. He is now 2 years off-therapy with clinical remission at the plaque, while the macules on the back remain unchanged.

Figure 1

(a, d) Clinical photograph showing cutaneous lesion before and after radiotherapy; (b) photomicrograph of skin biopsy (hematoxylin and eosin, 200×) showing dermal infiltration by atypical lymphocytes with epidermotropism; inset shows immuno - positivity for CD3; (c) pre - therapy PET - CT image showing intense FDG uptake over skin of anteromedial aspect of left leg; (e) PET - CT after radiotherapy showing resolution of FDG uptake

There are isolated case reports on role of PET-CT in cutaneous T-cell lymphoma (CTCL) and its most common subtype, MF.[1-3] In a series of 13 patients of CTCL (11 with MF), FDG uptake was negative in all cases with stage IA disease while it was positive in stage IVA disease.[4] In another report of 19 patients of CTCL (5 with MF), the highest accuracy of PET-CT was for detection of metastatic disease, especially at restaging (sensitivity and specificity of 100%).[5] Among 13 MF/Sezary syndrome patients, 2 patients with neoplastic involvement of LN would have been incorrectly staged as LN-negative in the absence of PET.[6] Higher standardized uptake values were noted in higher LN grades. MF is rare in childhood, and none of the published reports include any pediatric patient. In our case, PET showed uptake at the plaque, while excluding any LN or visceral involvement, and documented remission after irradiation. The macules were PET negative throughout.

We wish to highlight that PET-CT may be valuable in baseline evaluation and restaging in MF for plaque, tumor, or LN. However, it may be inferior to clinical examination in mapping the extent of cutaneous involvement, particularly when there are macules or thin plaques.