Unusual localization of multiple myxoid (mucous) cysts of toes
From the Dermatology Department1, Orthopedics and Traumatology Department2, and Pathology Department3, Sisli Etfal Research and Training Hospital, Istanbul, Turkey. email@example.com
Myxoid cysts of fingers and toes are observed frequently on the lateral or dorsal aspects of the distal digits. They are usually solitary nodules. Both subungual localization and multiplicity are quite rare. We present a 74-year-old woman with digital subungual mucous cysts located on all toes.
Digital mucous cysts commonly present as translucent nodules arising over the proximal nail fold or the distal interphalangeal joint. Less common locations are dorsal aspect of nail plate and beneath the nail. There are limited published data for the subungual localization for the subungual myxoid cyst .
We report a woman with subungual myxoid cysts located in both feet.
A 74-year-old woman was referred to our clinic with a 4-year history of solitary, clear nodules with wart-like projections located beneath the nails of both feet. There were verrucoid lesions on the proximal regions of some distal interphalangeal joints as well. She was initially presented with similar lesions to our dermatology clinic 5 years prior. An excisional biopsy had been obtained from the nodule just beneath the nail and histopathological examination had revealed the characteristic features of a myxoid cyst. She was treated by cauterization under local anesthesia. Following this procedure, all the cysts of both feet recurred at 1 year and the patient was reevaluated.
Dermatological examination revealed solitary nodules with wart-like projections, with diameters of 2-15 mm, on the dorsal aspects of all toes of both feet. All nails were dystrophic associated with these space occupying lesions. No discoloration was seen (Figs. 1 and 2). There were also verrucoid lesions on the proximal regions of some distal interphalangeal joints. After incision of these lesions a gelatinous material could be expressed. One of these cysts was removed by excisional biopsy. Histopathological examination showed hyperkeratosis in epidermis, keratin plugs, focal hypergranulosis and cystic spaces in subepithelial region (Figs. 3 and 4). The biopsy was interpreted as digital verrucoid mucous cyst. All the laboratory and radiological investigations were normal.
Digital mucous cysts are almost translucent, round to oval, soft or fluctuant, 3-10 mm cystic nodular lesions of the thumbs and fingers [2, 3, 4]. The epithelial surface of cysts may be smooth or verrucous. These cysts are usually located on the dorsal aspect of distal interphalangeal joints and less frequently the metacarpophalangeal joints. Common or typical presentations are solitary nodules (rarely multiple) located between the crease overlying the distal interphalangeal joint and the proximal nail fold. Subungual localizations, as seen in our patient, are uncommon, although de Berker et al.  emphasized that the small number of reports subungual myxoid cysts (SMC) might not reflect its real prevalence and lack of awareness of its clinical features contributes to infrequent diagnosis. In fact, some benign tumors (such as glomus tumor and neurofibroma), and malignant tumors (such as malignant melanoma) may cause difficulties in differential diagnosis. Verruca vulgaris is also in the differential diagnosis of the cysts in our patient. As documented by De Berker, there may be accompanying changes of nail curvature, nail integrity, and lunula color. However, these are not specific for SMC. Diagnosis is confirmed by histopathologic analysis, roentgenograhy and MRI. Histopathological analysis shows a cystic space without a cystic lining (pseudocyst) and frequently it is surrounded by compressed connective tissue. This cystic space contains mucinous material that stains with Alcian blue and colloidal iron [6, 7].
Hyde apparently provided the first discussion on the origin of myxoid cysts in the literature . There have been two described types: myxomatous type and ganglion type. The myxomatous type is analogous to focal mucinosis in which fibroblasts overproduce hyaluronic acid leading to a decrease of collagen formation. In the ganglion type, hyaluronic acid is derived from the joint fluid [2, 6, 8]. In both types, trauma and chronic pressure has been implicated for the cyst formation .
Trauma may be implicated as a triggering factor for the connective tissue degeneration of the distal aspects of the toes in our patient Nevertheless, why our patient had near simultaneous involvement of all toes in the same localization with verrucous component is unexplained.
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