The Diagnosis: Myxoid Cyst
Myxoid cysts, often called ganglion cysts or mucous cysts, are smooth translucent nodules that arise between the dorsal aspect of the distal interphalangeal joint and proximal nail fold.1 Lesions often have an associated distal depression or groove on the affected fingernail and typically appear on the middle and index fingers between the fourth and seventh decades of life.2,3 Acute lesions may present as tender nodules, whereas gradually developing lesions tend to be painless.3 Trauma to the distal interphalangeal joint, degenerative processes, and osteoarthritis may increase hyaluronic acid production and allow synovial fluid to escape the joint space, accumulating in the surrounding tissue. Subungual localization of a mucous cyst is rare and may be difficult to diagnose.4 The differential diagnosis includes benign and malignant tumors such as periungual fibroma, glomus tumor, basal cell carcinoma, squamous cell carcinoma, and amelanotic melanoma.5 Our patient declined treatment with cryotherapy or intralesional steroid injection and drainage. He was referred to the orthopedic surgery department for surgical removal of the cyst and imaging studies. Radiographs of the right thumb revealed severe osteoarthritis of the distal interphalangeal joint, demonstrating the association of digital mucous cysts.