A 76-year-old white woman presented to the dermatology clinic with a papule on the dorsum of the left third digit, near the proximal nail fold, causing nail dystrophy with a longitudinal groove.
The patient’s medical history was significant for osteoarthritis, and she had a dermatologic history of actinic keratosis, basal cell carcinoma, and seborrheic keratosis. The papule had been present for several months. It was asymptomatic, without ulceration, discharge, pain, or functional limitations. The patient was concerned about potential malignancy and nail dystrophy.
No imaging or diagnostic tests were conducted. A clinical diagnosis of digital mucous cyst (DMC) was made. After discussing the diagnosis and treatment options, the patient opted for observation.
DMCs, also called myxoid cysts or myxoid pseudocysts, are papules or nodules occurring between the distal interphalangeal joint (DIP) and the proximal nail fold. DMCs range in size, with an average diameter of approximately 5 mm. They are most commonly located in the medial or lateral nail fold or under the nail plate.1
DMCs typically are painless but can cause epidermal ulceration or nail dystrophy. Coloration varies from skin-colored to reddish purple with polymorphic telangiectasias that blanch with pressure.2,3 Drainage of translucent mucinous material following excoriation is common.4 The most common nail changes caused by DMCs in the nail fold are longitudinal grooves (as in our patient’s case), concave canaliform dystrophy, and transverse lines.5
There are 2 histopathologic varieties of DMCs: dermal fibroblast-derived DMCs that contain mucin but lack a capsule (pseudocysts), and synovial-derived DMCs with a pseudocapsule (ganglion type).6 The latter type often contains a pedicle connecting to the synovial capsule of the DIP.1,7
The etiology of DMCs is unknown but may involve local inflammation of the tissue or joint. DMCs of both types typically present after 40 years of age and are associated with osteoarthritis and osteophyte formation in the DIP, suggesting that joint degeneration may contribute to cyst formation.1,5 However, osteophytes are not required for development, and the location of the DMC relative to the DIP does not reliably indicate histopathologic type.8 Multiple DMCs in a single patient could indicate trauma to the DIPs such as repetitive compression from an occupational task.9
The diagnosis of DMCs is clinical and is based on characteristic location, size, and coloration. Transillumination can be used to visualize the cystic space10 and rule out solid lesions. Magnetic resonance imaging (MRI) or ultrasonography are not indicated but can be useful in subungual presentations.1,11
Treatment options vary widely and can be chosen based on patient preferences and office equipment. Observation is recommended for asymptomatic lesions. Surgical excision is common, with a 16.7% to 22.5% recurrence rate after 1 year.8,12 Needling and expression can be performed in-office with sterile needling, with a success rate of approximately 70%,13 but requires repeated follow-up drainage and poses significant infection risk. This includes a risk of septic arthritis with communication to the DIP. DMCs of the ganglionic type can be treated with intra-articular dexamethasone and lidocaine, with a success rate of 52.2%.14, Other treatment options such as infrared coagulation15 and laser ablation16,17 require specialized equipment. Polidocanol injection has been successful, with resolution in 77.8% of patients at 12 weeks postprocedure.18 Long-term recurrence following polidocanol injection may be as low as 8.3% as assessed in a smaller cohort of patients.19
Because the differential diagnosis of digital tumors is broad,20 it is important to exclude malignant tumors, which was our patient’s concern. Transillumination increases the likelihood of a DMC versus a solid tumor. Ultrasonography, MRI, or biopsy can aid if the diagnosis is uncertain, particularly in cases with a subungual presentation.
Malignant lesions can present in the digit. Nodular basal cell carcinoma can present as pink papules with telangiectasias21 mimicking a DMC. Squamous cell carcinoma can present with erythema or scaling papules or plaques.22 Periungual squamous cell carcinoma is associated with human papillomavirus infection and often presents as treatment-resistant verrucae.23 Melanoma typically presents as a macule with irregular borders and multiple colors.24 However, biopsy may be needed to exclude amelanotic melanoma, which can present as an erythematous macule or plaque.24 Benign lesions of the digits with periungual presentation include verrucae and pyrogenic granulomas. Verrucae are often found on the hands with heterogenous coloration (mosaic pattern) and vascular structures including dotted and looped vessels visible with dermoscopy,25 which can mimic DMCs. However, hyperkeratosis is more likely with verrucae.25 Pyogenic granulomas can be associated with mechanical trauma of the digit but often present as exophytic ulcerated masses that are highly vascular,26 in contrast to a DMC.
Proper diagnosis of DMCs based on clinical presentation can avoid unnecessary testing and properly exclude both malignant and benign digital lesions. While there are a variety of options for treating DMCs, patients may elect conservative management of asymptomatic lesions following education and reassurance.
Zachary A. Curry, BS Center for Dermatology Research, Department of Dermatology, Wake Forest School of Medicine, Winston-Salem, North Carolina
Kathryn L. Anderson, MD Center for Dermatology Research, Department of Dermatology, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Steven R. Feldman, MD, PhD Center for Dermatology Research, Department of Dermatology, Wake Forest School of Medicine; Department of Pathology, Wake Forest School of Medicine; and Department of Social Sciences & Health Policy, Wake Forest School of Medicine, Winston-Salem, North Carolina