Incidence and mortality of relapsing polychondritis in the UK: a population-based cohort study.

OBJECTIVE Relapsing polychondritis is a rare disease characterized by cartilage inflammation. Our aim was to estimate the incidence, prevalence and mortality of relapsing polychondritis and describe the clinical features of relapsing polychondritis in a large population. METHODS All participants diagnosed with relapsing polychondritis were sampled from the Clinical Practice Research Datalink. Prevalence and incidence rates for 1990-2012 were estimated. Relative mortality rates were estimated in a time-to-event framework using reference UK life tables. A questionnaire validation study assessed diagnostic accuracy. RESULTS There were 117 participants with relapsing polychondritis ever recorded. Fifty (82%) of 61 cases were validated by a physician and unconfirmed cases were excluded. The analysis included 106 participants (42 men, 64 women) diagnosed with relapsing polychondritis. The mean age (range) at diagnosis in men was 55 (range 17-81) years and in women 51 (range 11-79) years. The median interval from first symptom to diagnosis was 1.9 years. The incidence of relapsing polychondritis between 1990 and 2012 was 0.71 (95% CI 0.55, 0.91) per million population per year. There were 19 deaths from any cause. There were 16 observed deaths eligible for survival analysis and 7.4 deaths expected for the UK population of the same age, sex and period. The standardized mortality ratio was 2.16 (95% CI 1.24, 3.51), P < 0.01. Respiratory disease, cardiac conditions and cancer were the most frequent causes of death. CONCLUSION The incidence of relapsing polychondritis may be lower than previously estimated, and diagnostic misclassification and delay are common. Mortality in relapsing polychondritis is more than twice that of the general population.