# Pachydermodactily – the great imitator of arthritis: a case series

## TL;DR

Pachydermodactyly is a rare, benign condition that mimics arthritis in adolescents, often leading to misdiagnosis and unnecessary treatments.

## Contribution

This study presents a case series and literature review to improve recognition of pachydermodactyly and reduce diagnostic errors.

## Key findings

- Seven patients showed soft tissue swelling around PIP and MCP joints, resembling arthritis.
- None met criteria for juvenile idiopathic arthritis after thorough evaluation.
- Symptoms were often mistaken for chronic inflammatory conditions, leading to delayed diagnosis.

## Abstract

Pachydermodactily is a rare digital fibromatosis of unknown origin, mainly affecting adolescent boys. It presents as symmetrical, painless thickening of the soft tissues, usually around the proximal interphalangeal joints (PIP). Patients often experience delayed diagnoses, receive unnecessary treatments, or are misdiagnosed with chronic inflammatory arthritis. Although the exact cause remains unclear, pachydermodactyly may be associated with repetitive mechanical trauma, such as rubbing or interlacing the fingers, which can lead to secondary skin thickening. Treatment is often not required given its benign prognosis, although some patients ask for therapy due to the cosmetic impact of the condition. The aim of this study was to present the characteristics of seven patients diagnosed with pachydermodactily at pediatric rheumatology outpatient clinics in Zagreb. Additionally, we performed a comprehensive literature review of reported cases published from 1975 to 2024 using PubMed and Google Scholar. The primary symptom observed was swelling of the soft tissues around the PIP and metacarpophalangeal joints, with some patients presenting with hyperkeratotic plaques resembling knuckle pads. One patient experienced hand pain. Clinical examination and diagnostic workup were performed (laboratory tests specific for rheumatologic diseases, radiological tests such as joint ultrasound, x-ray or magnetic resonance imaging, or skin biopsy) to exclude other conditions with similar clinical features and etiologies, such as juvenile idiopathic arthritis. None of the patients met the criteria for juvenile idiopathic arthritis according to the classification criteria of the International League of Associations for Rheumatology. Increasing awareness of pachydermodactyly and achieving accurate diagnoses can reduce unnecessary diagnostic tests, treatments, and patient anxiety.