A Teenage Guitarist's Swollen Fingers

A 15-year-old male presented to our hospital with suspected juvenile idiopathic arthritis (JIA). He had developed insidious bilateral swelling of the second and third proximal interphalangeal (PIP) joints 1 year earlier, with no identifiable precipitating factors by himself. There was no family history of dermatological disorders. On further inquiry, his leisure activity was playing the guitar. On clinical examination, he exhibited symmetrical swelling of the PIP joints in both hands without redness and tenderness (Figure 1). Laboratory tests showed normal inflammatory markers, with negative results for rheumatoid factor (RF), anti-cyclic citrullinated peptide (CCP) antibody, and anti-nuclear antibody. Magnetic resonance imaging (MRI) revealed no evidence of synovitis or abnormal bone marrow signals but demonstrated swelling of the subcutaneous tissue. Radiographs showed no significant joint involvement (Figure 2). A skin biopsy was done (Figure 3). Clinical appearance showing swollen finger, suspected juvenile arthritis, but the patient complained of no clinical symptoms, including pain, tenderness, or disabilities. Laboratory tests also indicated neither inflammatory signs nor immunological abnormalities. X-ray and MRI detected no synovitis and arthritis, but showed swelling of subcutaneous tissue (Figure 2). Histological examination revealed fibrosis with replacement of subcutaneous fat tissue. Higher magnification revealed mild epidermal acanthosis (Figure 3a) and fibrosis, with thickened collagen bundles surrounding eccrine glands, and no inflammatory infiltrates (Figure 3b). Based on these findings, a diagnosis of pachydermodactyly was established. Pachydermodactyly is a benign fibromatosis characterized by painless, localized thickening of the skin around the PIP joints 1. It presents as progressive spindle-shaped swelling along the dorsal and lateral aspects of the PIP joints, most commonly affecting the second to fourth fingers symmetrically, but joint function is preserved, and there is no pain or inflammation. It typically occurs in otherwise healthy adolescent males, with a reported male-to-female ratio of approximately 6:1 and a mean age of onset of 15.6 years 1-3. Repetitive mechanical stress is considered one of the causative factors. It has been reported that approximately 40% patients have found a variety of repetitive mechanical stress, for example, keyboard use, finger stretching, music instruments 4, computer gaming, cracking fingers 5, sports, rock climbing, and even cooking 6. Playing guitar is considered a major contributing factor in this case. Several tests may be performed to diagnose pachydermodactyly, but no significant changes are observed except for histological examination. Histopathological examination of the affected skin shows epidermal acanthosis with mild hyperkeratosis 7. The dermis is markedly thickened, characterized by increased and irregularly arranged collagen bundles, particularly in the reticular dermis. Proliferation of fibroblasts is evident, while inflammatory cell infiltration is minimal or absent. No mucin deposition or significant vascular changes are observed. The adnexal structures are generally preserved. These findings are consistent with a localized fibrosing process rather than an inflammatory or scleroderma-like condition. Routine laboratory tests, including blood count, liver and renal function tests, and inflammatory markers, show no significant abnormalities 3. Autoantibodies such as RF and anti-nuclear antibody are negative, supporting the absence of systemic inflammatory or autoimmune disease. Radiographic and MRI examinations reveal no abnormalities in the underlying bone or joint structures 1, 3. There is no evidence of joint space narrowing, bone erosion, or periarticular inflammation. The soft tissue thickening is limited to the dermal and subcutaneous layers, consistent with the benign fibrotic nature of the lesion. Pachydermodactyly has to be differentiated from several conditions, such as JIA, rheumatoid arthritis (RA) or acromegaly. JIA and RA are the most important clinical differential diagnoses, but both should be accompanied by chronic inflammation. Typical features include joint swelling, tenderness, and restricted range of motion, often accompanied by systemic symptoms such as fever or malaise. Laboratory findings may demonstrate elevated erythrocyte sedimentation rate/CRP and positivity for anti-nuclear antibody, anti-CCP antibody, and RF. Acromegaly results from excess growth hormone secretion in adulthood, presenting with enlargement of the hands, feet, and facial features, often accompanied by joint hypertrophy. Isolated, localized thickening confined to the PIP joints without systemic changes is atypical. Since pachydermodactyly is a non-inflammatory and benign disorder, immunosuppressive therapy is unnecessary. Management is generally conservative, focusing on the avoidance of repetitive trauma if present. Spontaneous improvement may occur with the avoidance of repetitive mechanical stimulation, and specific therapeutic intervention is usually unnecessary 1, 8. In our case, we continue to follow up without any specific treatment, and have not found any significant improvement yet. To conclude, pachydermodactyly is a rare benign condition, but awareness of this entity is important for clinicians, as misdiagnosis may lead to unnecessary investigations or treatment. Maho Matsuo: writing – original draft preparation, conceptualization. Hiroaki Iwata: supervision. The authors received no specific funding for this work. The parents of minor patients have given written informed consent for their child's participation in the study, as well as for the use of their child's de-identified, anonymized, aggregated data, and case details (including photographs) for publication. Ethical Approval: not applicable. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.