Primary hypertrophic osteoarthropathy - a rare cause of pain and arthritis in children. Description of 5 cases.

Primary hypertrophic osteoarthropathy (PHOA) is a very rare disease. The typical triad of symptoms, i.e. digital clubbing, periosteal bone formation with bone and joint deformities and skin hypertrophy, may be accompanied by other specific conditions. In the majority of patients, the picture of the disease is incomplete. The dominant clinical symptom may be osteoarticular complaints. Moreover, the final confirmation of the diagnosis of the primary form of hypertrophic osteoarthropathy requires the analysis of much more frequent secondary causes of the disease. Diagnosing primary osteoarthropathy in children is particularly difficult. Some children report joint pain before the onset of the other symptoms of osteoarthropathy, while the physical and imaging examinations show features of arthritis. This can lead to misdiagnoses including the diagnosis of juvenile idiopathic arthritis (JIA) and the unnecessary use of immunosuppressive treatment. The present description of five patients from the Paediatric Rheumatology Department indicates diagnostic difficulties in children with PHOA. All of them were examined due to pain and features of arthritis. We observed an incomplete clinical picture of the disease. One patient required a revision of the previous diagnosis of JIA and discontinuation of ineffective treatment with disease-modifying antirheumatic drugs (DMARDs). PHOA should always be considered in the differential diagnosis of arthritis in children, due to the slow and often atypical development of symptoms, including the presence of pain and arthritis as the predominant symptom of the disease.