Arthropathy in a Pediatric Cystic Fibrosis Patient

Introduction: Cystic Fibrosis (CF) arthropathy is a uncommon presentation in CF patients with a prevalence of 2-9%[1], with a mean age of onset of 16. Risk of CF arthropathy increases with age, female sex and exacerbations of CF. Due to its rarity, both the disease and treatment of CF arthropathy pediatric patients is poorly defined.

Case Description: A 6-year-old male with a history of CF presented with a three-day history of right foot pain, bruising, and episodic fevers. Laboratory testing showed an elevated erythrocyte sedimentation rate, C-reactive protein, but normal complete blood count. Imaging of the involved foot showed no osseous abnormalities and no signs of osteomyelitis on x-ray or magnetic resonance imaging. Pulmonary function testing indicated a mild decreased in the predicted FEV1%. The patient was diagnosed with CF arthropathy and was managed with ibuprofen. The symptoms resolved spontaneously with no evidence of arthropathy at the subsequent encounter.

Conclusions: Literature on CF arthropathy is limited due to its rarity, especially for young children. This case serves to illustrates the clinical presentation, diagnosis, treatment, and outcome of CF arthropathy in a pediatric patient.

Discussion: Currently, CF arthropathy is not formally defined, and the disease process, and cause are still being investigated[3]. CF arthropathy is a periodic, self-limited, inflammation or periarticular erythema of the joints of CF patients that does not correlate with rheumatic disease [1,2]. The presentation is typically asymmetric involving one or more joints, most commonly the knee [1,2]. CF arthropathy can present with cutaneous findings like erythematous maculopapular eruption, purpura of legs, erythema nodosum, and cutaneous vasculitis[4]. Some patients can also present with fever and Raynaud’s phenomenon[1]. Since CF arthropathy remains a diagnosis of exclusion, other causes of arthropathies should be ruled out including drug-induced arthropathy, gout, pseudogout, and rheumatoid arthritis[5].Depending upon the severity of presentation, and the number of joints involved, providers should take a different approach to diagnosis. In cases where a single joint is involved, a CBC, acute phase reactants such as CRP, examination of synovial fluid, and serology are recommended[2,5].Additional workup can be done with ultrasound (US) and MRI to identify inflammatory changes in the joints. Treatment of CF arthropathy is currently not well established and most patients are treated with non-steroidal anti-inflammatory medications and bed rest[3].The pathogenesis of CF arthropathy is unknown. Most of the current hypotheses regarding CF arthropathy are immune system mediated. Another hypothesis suggests that bacterial antigens may create an inflammatory response affecting tissue directly.

Conclusion: CF arthropathy is a rare complication of CF, presenting with periodic spontaneous joint pain and inflammation that is not explained by injury, osteomyelitis, or other inflammatory diseases. This case highlights the diagnosis and treatment of CF arthropathy, and serves as a reminder that occurrence in young children is possible.