Purpose or Case Report: Primary Hypertrophic Osteoarthropathy (PHO) is a self-limiting, rare condition that emerges in the pediatric or adolescent years with a predilection for males, especially of African descent. It is often accompanied with symptoms of arthralgias, hyperhidrosis, and acne. PHO manifests in various forms, with the complete presentation being the most severe, characterized by facial coarsening, periostosis, and digital clubbing. In contrast, incomplete PHO spares the scalp, and forme fruste PHO exhibits clubbing and facial coarsening with minimal periostitis, duly setting it apart from secondary hypertrophic osteoarthropathy that is commonly associated with cardiac or pulmonary conditions. Genetic mutations in the 15-hydroxyprostaglandin dehydrogenase (HPDG) and solute carrier organic anion transporter family 2A1 (SLCO2A1) genes introduce variability in the inheritance patterns of PHO. HPDG-related PHO is typically autosomal recessive, while SLCO2A1-related PHO can be either autosomal recessive or dominant. These mutations elevate prostaglandin E2 levels, intensifying osteoclast activity, and causing bone resorption, which, in turn, triggers VEGF release and leads to vascular hyperplasia, bone disturbances, and edema. A common radiographic finding is acroosteolysis, and key features to differentiate PHO from other causes of acroosteolysis include terminal tuft resorption and periostitis. Other distinctive radiographic findings in PHO include terminal tuft resorption in fingers and toes and shaggy periostosis in long bone diaphyses. Treatment options include nonsteroidal anti-inflammatory drugs (NSAIDs) and bisphosphonates for pain relief and cosmetic surgery if desired. We will present a few cases from our institution to review classic imaging findings, diagnostic workup, and management.

Teaching Points:
1. Understand the clinical variability in presentations of Primary Hypertrophic Osteoarthropathy (PHO).
2. Recognize the genetic basis of PHO and appreciate the variable inheritance patterns associated with the HPDG and SLCO2A1 genes.
3. Identify the distinct radiological features of PHO, including terminal tuft resorption and shaggy periostosis, enabling accurate diagnosis and differentiation from other conditions.
4. Emphasize the importance of early diagnosis, highlighting how prompt recognition of clinical and radiographic features can enhance patient outcomes and mitigate complications.
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