To the Editor:
We read with great interest the recent work by Cullen et al1 on superficial acral fibromyxoma (SAF) published in the January issue of American Journal of Dematopathology, in which the authors evaluated clinical, histopathologic, and immunohistochemical features of 13 cases of SAF. We would like to present our own findings from a recent case of a patient with an SAF with an unusual cartilaginous aspect, which, to the best of our knowledge, has never been reported.
In this particular case, a 57-year-old woman presented with an asymptomatic, slow-growing tender mass on the left fifth toe. The lesion had been present for 4 years as a well circumscribed, erythematous nodule with a peripheral collarette (Fig. 1). On histopathological examination, the lesion consisted of a well-limited, nonencapsulated dermal tumor composed of spindle cells arranged in a fascicular pattern and immersed in a myxoid stroma (Fig. 2). In the center of the lesion was a cartilaginous differentiation with lobules of mature chondrocytes with round or oval nuclei and a scarce cytoplasm immersed in a chondroid matrix (Fig. 3). Fusiform cells showed strong positivity for CD34. The chondrocytes did not express CD34 but did express S-100 protein. We diagnosed the lesion as SAF with cartilaginous metaplasia.
Our clinical and histopathological differential diagnosis included subungual soft tissue chondroma, a rare benign tumor composed of a small nodule of cartilage with no connection to the underlying bone or periosteum. It typically occurs in distal extremities of middle-aged patients for which only a few cases have been reported.2–7 Subungual soft tissue chondromas may cause nail deformities. Histopathologically, soft tissue chondroma consists of lobules of mature chondrocytes immersed in a cartilaginous matrix but lacks the CD34-positive spindle cell proliferation observed in this case of SAF. Subungual exostosis (subungual osteochondroma) is a relatively frequent lesion that develops in distal phalanges of the fingers and toes, particularly on the big toes. It presents as a slow-growing, flesh-colored or erythematous tender nodule under the nail plate. It consists of a central core of mature bone surrounded by a coating of mature cartilage. Endochondral ossification proceeds from base to cap. Thus, immature lesions have only a thick cartilage cap because endochondral ossification has not readily occurred.8 The diagnosis may be difficult in these cases but the spindle cell proliferation encountered in SAF is lacking.
The authors thank Dr. Luis Requena for reviewing the slides of this case.
1. Cullen D, Díaz Recuero JL, Cullen R, et al. Superficial acral fibromyxoma: report of 13 cases with new immunohistochemical findings. Am J Dermatopathol. 2017;39:14–22.
2. Connolly M, Intzedy L, Collins C, et al. Lateral views and subungual soft-tissue chondromas. J Am Acad Dermatol. 2008;58:S58–S59.
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8. Ilyas W, Geskin L, Joseph AK, et al. Subungual exostosis of the third toe. J Am Acad Dermatol. 2001;45:S200–S201.