Knuckle pads – a rare finding

Abstract

Knuckle pads are rare harmless subcutaneous nodules that must be differentiated from joint disease of the proximal interphalangeal or rarely of the metacarpophalangeal joints as well as from other masses of the paraarticular tissues. We present a case of an otherwise healthy 36-year-old woman presenting with bilateral knuckle pads located at the dorsal aspect of the proximal interphalangeal joints. No predisposition to a specific musculoskeletal disorder was noted. Ultrasound revealed well-delimited subcutaneous hypoechoic masses without internal flow signals at color Doppler. Histology showed proliferation of myofibroblasts with a decrease of elastic filaments in the deep dermis. The clinical picture, the family history in addition to the histology allowed us to make the diagnosis of knuckle pads. We present the ultrasound findings of knuckle pads and discuss the differential diagnosis of a “swelling” in the dorsal region of proximal interphalangeal joints and metacarpophalangeal joints.

A novel treatment for idiopathic knuckle pads with cantharidin‐podophylotoxin‐salicylic acid

“…Clinically, they present as painless, well‐circumscribed, mobile subcutaneous nodules that typically involve the dorsum of the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints. Motion of the affected joint is generally not restricted …”

“…Primary KP are seen in children and young adults and are mostly idiopathic; in older patients, they are associated with fibrosing disorders such as Dupuytren's contracture, Ledderhose's syndrome, and Peyronie's disease. Secondary or acquired KP appear in response to repetitive trauma, having been described in patients with obsessive‐compulsive disorder, bulimia, or secondary to athletic or professional activites …”

Imaging Features of Knuckle Pads

“…There is an association with other fibrotic disorders, such as palmar (Dupuytren’s disease) and plantar fibromatosis (Ledderhose’s disease). In the paediatric population, knuckle pads have been described as being idiopathic [ 1 ].…”

“…On Doppler ultrasound, vascularization is absent or restricted to the periphery of the lesion. The adjacent soft tissues, joints and tendons are not involved [ 1 ].…”

“…The differential diagnosis includes Bouchard and Heberden’s nodes of osteoarthritis, rheumatoid nodules, gouty tophi and giant cell tumor of the tendon sheaths [ 1 ]. Plain radiographs may be helpful in the differential diagnosis with osteoarthritis, gout and rheumatoid arthritis.…”