Unilateral Pachydermodactyly in a Young Female: A Rare Diagnosis Requiring Novel Clinicopathological Correlation.

Pachydermodactyly (PDD) is a rare, non-inflammatory fibromatosis characterized by thickening of the proximal interphalangeal joints, typically presenting bilaterally in adolescent males. We report a case of unilateral pachydermodactyly transgrediens in a 14-year-old female with a one-year history of painless, doughy thickening and hyperpigmentation on the left proximal interphalangeal joints. Comprehensive labwork and imaging studies revealed no evidence of inflammatory joint disease, leading to further investigation by biopsy to confirm the suspected diagnosis of unilateral pachydermodactyly and to exclude other diagnostic possibilities. Histopathologic examination revealed findings consistent with PDD: epidermal hyperkeratosis, acanthosis, and disorganized dermal collagen bundles without significant inflammation or sclerosis. This case emphasizes the importance of recognizing the typical clinical, histopathologic, and radiographic features of pachydermodactyly, particularly highlighting the absence of specific histopathological features such as inflammation, significant mucin deposition, increased cellularity, fibrosis, or sclerosis. Increased awareness of the varying presentations of PDD may aid in timely diagnosis and help avoid unnecessary evaluation and treatment of more serious conditions that mimic PDD. Our case highlights the importance of clinicopathological correlation in diagnosis PDD, especially in atypical presentations, and aims to increase awareness of this entity among dermatopathologists.