Inflammatory mixo-hyaline tumor of distal extremities - a rare sarcoma simulating benign diseases.

Dear Editor,

We present here a case of inflammatory mixo-hyaline tumor, a low degree sarcoma that, due to its rarity and because it has a broad differential diagnosis, tends to be frequently confused with benign diseases. In addition, the diagnosis is complex due to the peculiar histopathological characteristics of this sarcoma. A surface biopsy can lead to errors in the diagnosis resulting from confusion with mixoid benign tumors or inflammatory diseases.[1,2]

A female patient, 61 years of age, had been undergoing follow-up for palmoplantar psoriasis since 55 years of age. Three years ago, in a routine doctor's appointment, she complained of a painless bulge and important dystrophy of the fingernail of the third left finger, whose histopathological result of the incisional biopsy revealed a mesenchymal proliferation comprised of fusiform cells with pleomorphic areas, suggestive of pleomorphic fibroma. The lesion was excised. Two years ago, the patient again reported a bulge in the distal phalange involving the proximal fingernail of the same finger. The patient underwent a new excision of the lesion, and the histopathological result was compatible with a hybrid cyst (epidermal and trichilemmal). In March 2015, she came to her follow-up appointment presenting a friable erythematous nodule on the side of the fingernail of approximately 2 cm. Also observed were a bulge in the distal phalange and marked dystrophy of the fingernail (Figure 1). A new incisional biopsy was performed, whose histopathological findings were compatible with inflammatory mixo-hyaline sarcoma, which was also confirmed by immune-histochemical analysis (Figures 2 and 3). The patient was referred to the oncology service to carry out a more in-depth surgical approach.

Figure 1

Friable erythematous nodule in lateral fingernail, bulge of distal phalange and marked dystrophy of the fingernail

Figure 2

HE – Magnification of 200x: Proliferation of mesenchymal, pleomorphic cells, dispersed throughout the dermis and infiltrate. Mixed inflammatory

Figure 3

HE – Magnification of 400x: Atypical neoplastic cells, with thin cytoplasm, large nuclei with open chromatin and evident nucleolus, some surrounded with halos and forming structures that have an appearance similar to virocytes or Reed-Sternberg cells. Dense inflammatory infiltrate consisting of lymphocytes and neutrophils

Inflammatory mixo-hyaline of the distal extremities, also known as acral mixo-inflammatory fibroblastic sarcoma, is a low-degree sarcoma that is extremely rare, first described by Montgomery in 1997. This sarcoma has a tendency for local recurrence, especially when only partially excised, through it possesses a low metastatic potential. It occurs primarily in adults and appears as a painless mass in the distal region of the limbs. The upper limbs are more affected than the lower limbs, with the fingers and hands being the most commonly affected. The clinical diagnosis of this tumor before biopsy is generally that of an inflammatory benign lesion (60% of the cases), and its differential diagnosis is performed with reactive processes and neoplasias, such as mixo-fibrosarcoma, epithelioid sarcoma, Hodgkin's disease, and superficial acral fibromyxoma.[1-3] In the reported case, the tumor appeared as a painless bulge and dystrophy of the fingernail. After two apparently macroscopically complete excisions, a new local recurrence appeared and was submitted to an incisional biopsy. Histologically speaking, the sarcoma of the distal extremities appears in three main types of tumor cells. The first type is similar to virocytes or to Reed-Sternberg cells; the second typed contains multivacuolated cells imitating pleomorphic lipoblasts; and the third type contains gigantic cells with characteristics of emperipolesis.[3,4] Under histochemical staining, these tumors express vimentin and can have a CD68 focal coloration.[4] In our case report, in the incisional sample, binucleated cells could be observed with evident nucleolus, similar to Reed-Sternberg cells surrounded by either a mixoid or a fibrous matrix and with permeable blood vessels (Figures 2 and 3). Immunohistochemical analysis was focally positive for actin of the smooth muscle and negative for Alk-1, cytokeratins, S-100, S-100 protein, human melanoma black-45 (HMB-45), and Melan-A. The rarity and broad variety of the morphologies make it important to understand the inflammatory mixo-hyaline tumor, a low-degree sarcoma that can simulate more aggressive sarcomas or imitate an inflammatory process through an extreme scarcity or clear absence of characteristic lesional cells. However, regardless of the histological findings, a complete excision, preferably with free margins, is the most efficient approach to reduce the incidence of the local recurrence of the disease, which is the main cause of morbidity associated with the tumor. In addition, adjuvant therapy, such as radiation, can be considered for those patients with positive surgical margins, especially if the tumor contains atypical histological characteristics.[1,3,5]