Abstract

A 43-year-old woman presented to her dermatologist with asymptomatic nodules over her proximal interphalangeal joints. She denied significant friction, trauma, or pressure to those areas and there was no family history of fibromatosis. On examination, there were bilateral and symmetrical, ill-defined, skin-colored to slightly pink, semi-firm, mobile, nontender plaques overlying most extensor proximal interphalangeal joints (PIP) bilaterally, without contractures of either hands. Her palms were uninvolved. A punch biopsy of a lesion over the right fourth PIP revealed collagenized bands of myofibroblasts in the deep dermis and subcutis that were characteristic of fibromatosis. Primary knuckle pads are a variant of cutaneous fibromatosis that can be associated with genetic diseases including palmar fibromatosis (Dupuytren's contracture), plantar fibromatosis (Ledderhose's disease), camptodactyly, epidermolytic palmoplantar keratoderma, Bart–Pumphrey syndrome, and acrokeratoelastoidosis of Costa. As in all fibromatoses, primary knuckle pads are myofibroblastic proliferations that must be distinguished from secondary knuckle pads caused by friction and manifest as hyperkeratotic papules without dermal involvement.