Pachydermodactyly: A Case Report

Summary: A 15-year-old boy with autism spectrum disorder presented with long-standing proximal focal enlargement of multiple fingers on both hands, accompanied by occasional soreness. Clinical exam revealed several ill-defined, soft, slightly mobile subcutaneous nodules of the affected digits. The initial clinical differential diagnosis included knuckle pad, self-healing juvenile cutaneous mucinosis, vascular malformation and rheumatic nodule. Ultrasound showed regions of indistinct deep soft tissue fullness involving the proximal fingers. Two punch biopsies were performed and histopathological examination showed orthohyperkeratosis and papillomatosis of the epidermis with mildly thickened collagen in the dermis and increased dermal fibrosis composed of plump interstitial fibroblasts. Colloidal iron stain demonstrated an increased amount of dermal mucin in the deep dermis. CD34 highlighted the stromal fibroblasts, while SMA was negative throughout the dermis. The clinical presentation combined with histopathologic findings were consistent with a diagnosis of pachydermodactyly. Pachydermodactyly is a rare, typically asymptomatic and benign fibromatosis located around the proximal interphalangeal joints. It is often misdiagnosed as juvenile idiopathic arthritis leading to unnecessary treatments and anxiety in patients. Knowledge about this condition is limited, increasing the likelihood of its underdiagnosis. We present this interesting case of pachydermodactyly with histopathological findings.