Peripheral eosinophilia in children with transient synovitis of the hip: 7-year experience from a single centre in New Zealand

PURPOSE Hip pain with limping is a common presentation in childhood. The most common diagnosis in young children is transient synovitis of the hip (TSH), a benign and self-limiting condition. In our clinical practice, we observed eosinophilia in children presenting with irritable hip more commonly than would otherwise be expected. The aims of this study were to assess the prevalence of eosinophilia in children with TSH, and to evaluate the clinical outcomes of this sub-group of patients. METHODS This study retrospectively examined the data of all paediatric patients admitted to Christchurch Public Hospital, Christchurch, New Zealand. TSH cases were compared with age- and sex-matched controls. RESULTS A total of 103 patients were included. Compared with controls, TSH patients had significantly higher eosinophil counts (303 ± 236 vs. 380 ± 337 cells/μL, respectively, p = 0.049). Fourteen patients (15.6 %) had eosinophilia, with a mean eosinophil count of 986 (±321) cells/µL. Children who had eosinophilia did not differ from the rest of the sample in their age (mean 4.6 vs. 4.4 years, p = 0.74) or ethnicity (85.7 vs. 85.5 % European, p = 0.99). Eosinophilic children were not more likely to be atopic (i.e. have history of allergic rhinitis, asthma and/or eczema) than non-eosinophilic children (21.4 vs. 10.5 %, p = 0.37). There was a shorter hospital stay in eosinophilic children (mean 16.3 ± 6 h) than in non-eosinophilic children (mean 21.5 ± 18.8 h), although this was not statistically significant (p = 0.058). CONCLUSIONS To the authors' knowledge, this is the first study to explore the relationship between TSH and eosinophilia. We found a sizeable minority (15.6 %) of children with TSH to have eosinophilia. While the difference in hospital stay was not statistically significant, a correlation between peripheral eosinophilia and length of hospital stay of TSH patients is possible. Whether this correlation is clinically meaningful remains to be answered. LEVEL OF EVIDENCE Retrospective prognostic study; level II.