Nail Unit Glomus Tumor with Myxoid and Symplastic Change Presenting with Longitudinal Erythronychia Open Access

A 41-year-old female presented to her dermatologist’s office for evaluation of the left thumbnail. There was a 10-year history of longitudinal erythronychia of the left thumbnail, and recently there was the onset of associated pain of the nail with palpation and pressure. The patient denied a history of trauma or infection in the affected nail. An X-ray of the nail did not demonstrate underlying bone or soft tissue pathology. Over the next few months, the lesion progressed, with deepening of the erythronychia, formation of a longitudinal ridge in the nail plate, and progressive increase in pain intensity (Fig. 1). A biopsy of the left thumbnail unit was performed.

Sections of this nail unit specimen revealed a deep dermal nodule lying beneath the associated matrix epithelium which was comprised of eosinophilic, cuboidal cells forming vascular luminae. Foci of myxoid stromal changes were present. Scattered enlarged, atypical cells with hyperchromatic and irregularly contoured nuclei were present. However, extensive examination of the lesional cells did not demonstrate mitoses. Focally prominent nucleoli were also present in these cells. Immunohistochemical analysis demonstrated the lesional cells to be highlighted with smooth muscle actin. A PHH3 stain did not highlight the lesional cells. These features were diagnostic of a nail unit glomus tumor with myxoid and symplastic change (Fig. 2-7).

Glomus tumors are unusual soft tissue tumors, which are most frequently encountered in the nail unit. Generally, these lesions are straightforward to diagnose by histopathology, but rare variants such as the variant described here, with myxoid and symplastic change, can cause diagnostic difficulty. The typical form of glomus tumor is a well-circumscribed lesion containing capillary-sized vasculature surrounded by glomus cells. A hyalinized or myxoid stroma within the parenchyma of a glomus tumor is an unusual feature. The monomorphous appearance of glomus cells, which are small polygonal cells with pale cytoplasm and typical round nuclei, is traditionally the most dependable clue to distinguishing this tumor from others with a comparable growth pattern [1, 2]. Rarely, glomus tumors can display unusual histologic characteristics with significant nuclear atypia [1]. Folpe et al. [3] studied a series of 52 cases of glomus tumors with atypical features and designed a classification scheme which includes four groups. The malignant glomus tumor has a distinct risk of metastasis. These lesions fulfill at least one of the following criteria: increased depth and size more than 2 cm, the presence of atypical mitotic figures, or a combination of moderate-to-high nuclear grade and mitotic activity (5 mitoses/50 high-power fields). Lesions exhibiting a combination of atypical features but which are not able to meet the minimum definition criteria of malignant glomus tumor are labeled “glomus tumors of uncertain malignant potential.” The other group lacking criteria for malignant glomus tumor or glomus tumor of uncertain malignant potential is classified as “glomangiomatosis” and is characterized by diffuse infiltrative growth, resembling angiomatosis, with excess glomus cells. Lastly, glomus tumors having marked nuclear atypia in the absence of any other criteria for malignancy have been clearly shown to be benign and have been classified as “symplastic glomus tumor” [3].

In general, glomus tumors are most often subungual in location and commonly present as a small, slightly raised, violaceous or erythematous, painful nodule that can raise and distort the nail [4]. Localized tenderness and severe pain exacerbated by physical pressure or cold temperature are highly suggestive of this tumor. As with our case, glomus tumors may also present with localized longitudinal erythronychia, but this is a less common presentation [5-7]. In a Mexican study that examined all nail unit tumors in their health system, glomus tumor was 6th in frequency. Of their 13 cases, all demonstrated erythronychia and distal onycholysis but none displayed myxoid or symplastic change on histopathologic analysis [8]. Prominent myxoid change has been documented in glomus tumors [9, 10]. This is also true of symplastic change, but there are only a few sources in the literature that demonstrate the combination of myxoid and symplastic change within a single glomus tumor specimen [1, 11]. Kamarashev et al. [1] identified a lesion consistent with a symplastic glomus tumor with myxoid change, which presented with a pinpoint bluish discoloration of the nail associated with paroxysmal pain in the finger upon cold exposure. Mentzel et al. [11] also identified a lesion with both symplastic and myxoid change; however, it was not subungual in location.

It is worth noting that in an early case series, glomus tumors with histologic findings of symplastic glomus tumor were described as “epithelioid glomus tumors” in 1995 [2]. That series presented 5 cases, none of which were in the nail unit. This entity of epitheloid glomus tumor is histologically consistent with what is now referred to as symplastic glomus tumor.

Symplastic changes have been identified in several other tumors including giant cell tumors of bone, capillary arteriovenous malformations, and uterine leiomyomas. The common theme is that the nuclear atypia and pleomorphism mimic a malignant process but are decidedly benign in clinical course [12-14]. The high-grade nuclear atypia that characterizes these tumors is believed to be a manifestation of cellular degeneration and senescence rather than malignant transformation [1, 3]. Importantly, symplastic glomus tumors are consistent with this and have not been shown to metastasize or recur after excision [3].

In summary, we present a case of a subungual glomus tumor with myxoid and symplastic change that had a clinical presentation of longitudinal erythronychia. This particular variant with both symplastic and myxoid change is rare and needs to be recognized as a benign entity by dermatopathologists to avoid the overdiagnosis of atypia and overly aggressive treatment. Of those glomus tumors with both myxoid and symplastic change, this tumor is the only one to have a clearly documented clinical presentation with longitudinal erythronychia. This clinical appearance is consistent with routine glomus tumors. Given the excellent clinicopathologic correlation of this case, we believe that glomus tumor with myxoid and symplastic change should be included to the clinical differential diagnosis of monodactylous longitudinal erythronychia.

The manuscript was prepared in compliance with all ethical and confidentiality guidelines and principles. The patient gave her consent.

The authors have no conflicts of interest to disclose.