Tillett W, et al. – The authors aimed to determine the time interval between the onset of psoriasis and psoriatic arthritis (PsA) in the UK primary care setting and in well–classified secondary care cohort. They observed a similar distribution for the time interval between psoriasis and arthritis in the UK Clinical Practice Research Datalink (CPRD) and secondary care cohort. These findings would aid in forming new screening strategies.

Methods

• Patients with PsA and/or psoriasis were identified in the UK Clinical Practice Research Datalink (CPRD). 
• The secondary care cohort included patients from the Bath PsA longitudinal observational cohort study.
• For incident PsA patients in the CPRD who also had a record of psoriasis, the time interval between PsA diagnosis and first psoriasis record was calculated. 
• In the Bath cohort, comparisons were made with the time interval between diagnoses.

Results

• In the CPRD there were 5272 eligible PsA patients.
• However, the Bath cohort consisted of 815 eligible PsA patients.
• Investigations showed that in both cohorts, the majority of patients (82.3 and 61.3%, respectively) had psoriasis before their PsA diagnosis or within the same calendar year (10.5 and 23.8%), with only a minority receiving their PsA diagnosis first (7.1 and 14.8%).
• Excluding those who presented with arthritis before psoriasis, the median time between diagnoses was 8 years [interquartile range (IQR) 2–15] in the CPRD and 7 years (IQR 0–20) in the Bath cohort.
• In the CPRD, 60.1 and 75.1% received their PsA diagnosis within 10 and 15 years of their psoriasis diagnosis, respectively; this was comparable with 57.2 and 67.7% in the Bath cohort.