Clinical expression, but not disease outcome, may vary according to age at disease onset in psoriatic spondylitis

ObjectivesTo investigate whether the clinical expression and disease outcome in psoriatic spondylitis (PsS) may vary according to age at disease onset.MethodsThis study included 70 patients from a unique outpatient spondylitis clinic followed on a regular basis with a standard protocol. Patients were diagnosed with PsS according to ESSG criteria plus radiographic sacroiliitis (SI). Outcome parameters included: disease activity, functional evaluation, radiological damage, mobility restriction, and enthesitis score. Patients were divided into those with disease onset before 40 years (young-onset PsS) and those with onset over this age (late-onset PsS). Clinical features and outcome parameters were compared between groups.ResultsThere were 44 men and 26 women. Thirty-nine (M:F ratio 1.8) patients had disease onset before 40 years and 31 (M:F ratio 1.6) over this age. HLA-B27 correlated with PsS susceptibility (34% vs 7%, RR 6.4, p < 0.0004), but it was found over-represented in young-onset PsS compared to late-onset cases (51% vs 13%, p = 0.001). Young-onset cases tended to have a higher frequency of family history (26% vs 13%), bilateral SI (62% vs 29%, p = 0.013), isolated axial pattern (31% vs 13%), and enthesitis (54% vs 29%, p = 0.09). In late-onset PsS there was a higher frequency of unilateral SI (71% vs 38%, p = 0.013), polyarthritis (45% vs 23%, p = 0.022), and silent axial disease (32% vs 10%, p = 0.022). Outcome parameters were similar between groups.ConclusionsClinical picture but not outcome parameters, varies according to age at disease onset in PsS. The correlation between HLA-B27 and young-onset PsS supports the notion that disease susceptibility and disease expression are not driven by the same gene in this entity.