Background/Purpose: Obesity is associated with an increased risk of developing psoriatic arthritis (PsA) in patients with psoriasis. This study aimed to assess whether obesity is associated with a distinct phenotype of PsA.

Methods: A cross-sectional analysis was performed among patients with early PsA (≤2 years from the diagnosis) from a large PsA clinic and compared them to patients with psoriasis alone (PsC). Patients with PsA met the CASPAR criteria. Patients with PsC were examined by a rheumatologist to exclude the presence of arthritis. The participants were assessed according to a standardized protocol. Demographic, clinical and radiographic information was retrieved from the clinic database. The primary predictor was Body Mass Index (BMI) at the first visit to the clinic that was classified to normal (BMI<25), Overweight (BMI 25-30), Obese (BMI>30). The association between BMI and clinical and radiographic outcomes was assessed using Cochran-Armitage and linear trend tests.

Results: A total of 305 early PsA and 498 PsC patients were analyzed. Higher BMI was associated with older age (years) at onset of PsA (Normal: 38±14, Overweight: 44±14, Obese: 47±11, p^trend<0.0001) and psoriasis (Normal: 27±17 years, Overweight: 29±15, Obese: 33±15, p^trend=0.009). A similar trend was observed in patients with psoriasis alone, higher BMI was associated with older age (years) at onset of psoriasis (Normal: 28±16, Overweight: 39±16, Obese: 32±16, p^trend =0.01). In addition, a longer delay (years) from the onset of symptoms to the time of the diagnosis was found in overweight and obese patients (Normal: 2.8±5.8, Overweight: 3.9±10, Obese: 6±9.4, p=0.02). No difference was observed in the pattern and severity of the skin, nail or joint manifestations across the three BMI groups. Patients with higher BMI were more likely to have new bone formation at the pelvic and heel entheses (each <0.001) however no difference was observed in the extent of radiographic erosive damage. The frequency of overweight and obesity was higher in PsA compared to psoriasis alone only among participants who were older than 40 years of age (Table 1) while no difference in BMI was observed among younger individuals.  

Conclusion: Obesity may mark a distinct phenotype of PsA. Higher BMI is associated with older onset of PsA and psoriasis. This finding may suggest that obesity predisposes to late-onset psoriatic disease but has little role in the development of early onset disease.