This is a digital mucous cyst, also known as a myxoid cyst. The clear to translucent appearance over a finger or toe joint is usually diagnosed clinically. If uncertain, a biopsy can confirm the diagnosis.
Digital mucous cysts are a type of ganglion cyst that is associated with trauma or arthritis in the toe joint. A microscopic opening in the joint capsule results in a fluid filled cyst in the surrounding tissue. If the cyst is ruptured, thick, gelatinous (sometimes blood-tinged) hyaluronic acid–rich fluid may escape. Sometimes, the cyst applies pressure to the nail matrix, causing a scooped out longitudinal nail deformity.
Digital mucous cysts more commonly affect the fingers than the toes. Although benign, patients may be bothered by the appearance of these cysts and their effect on nails. Observation is a reasonable approach. Rarely, digital mucous cysts resolve spontaneously.
Treatment options include cryotherapy, needle draining and scarification, and surgical excision with flap repair. Surgical excision may be performed quickly in the office and offers the highest cure rate of 95% in 1 study on fingers.1 Cryotherapy is successful in 70% of cases and needle drainage is successful in 39% of cases, but these modalities are quick and require minimal downtime.1
In this case, the patient was not significantly bothered by the lesion and was happy to forego treatment.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained). Dr. Karnes is the medical director of MDFMR Dermatology Services, Augusta, ME.