Derm Dx: Blue-purple macule beneath the nail

Glomus tumors are a rare benign neoplasm of glomus cells that most commonly present in young adults between 20 and 40 years of age.Although the pathogenesis is unclear, most glomus tumors occur in the subungual region of the fingernail, which...

Submit your diagnosis to see full explanation.

Glomus tumors are a rare benign neoplasm of glomus cells that most commonly present in young adults between 20 and 40 years of age.

Although the pathogenesis is unclear, most glomus tumors occur in the subungual region of the fingernail, which have the highest density of distribution of normal glomus cells. This finding suggests that many glomus tumors are neoplastic proliferations arising from pre-existing normal glomus cells.

Glomus tumors, however, have also been found at other sites where normal glomus cells have not been found, suggesting they may arise from other mesenchymal or smooth muscle cells.

Although glomus tumors show no gender predilection, digital subungual lesions are more common in females, and nondigital lesions are more common in males.

Clinically, solitary glomus tumors most frequently present as a skin-colored or blue-red papule or nodule measuring 1 to 20 mm in diameter. The most common site of occurrence of glomus tumors is the subungual region of the fingernail. Tumors may also occur on the hands and arms, especially the fingers and palms.

Glomus tumors are extremely tender to the touch and are associated with paroxysmal pain, usually in response to temperature and pressure changes. When the tumor is touched, the patient may experience severe, radiating pain.

When present under the nail plate, subungual glomus tumors present as a bluish tinge underneath the nail. Without treatment, glomus tumors may undergo progressive growth with ulceration or in extremely rare cases, undergo malignant transformation with metastasis.

Diagnosis of glomus tumors is by clinical presentation, imaging, and histology. MRI is usually the primary diagnostic modality of choice, and will demonstrate a strongly enhancing mass. Imaging may also be used to define the tumor before performing surgery.

Histologically, glomus tumors are a well-circumscribed proliferation of solid sheets of glomus cells clustered around a flattened endothelium-lined vessel. The glomus cells are round and arranged in distinct rows that resemble “strings of black pearls.”

Solitary glomus tumors are usually treated with complete local surgical excision, which provides complete relief from pain.

Christopher Chu, BS is a medical student at Baylor College of Medicine.

Adam Rees, MD is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.