The epidemiology and risk of mortality for patients with psoriatic arthritis

Prevalence and incidence of PsA in general population¹

In the general population, the prevalence of psoriatic arthritis (PsA) ranges from 0.1% to 1% worldwide. A high degree of variability has been observed between epidemiological studies, partly due to the geographic location and due to the use of different definitions of PsA. In Japan and Norway, the estimated prevalence of PsA has been recorded as 1 and 670 cases per 100,000, respectively. A high degree of variation in PsA incidence has also been found both between and within continents (Figure 1).

Figure 1. Incidence of PsA in the general population*

CASPAR, Classification of Psoriatic Arthritis; CI, confidence interval; ESSG, European Spondylarthropathy Study Group; ICD, International Classification of Diseases; M/F, male to female; M&W, Moll and Wright criteria; NR, not reported; PsA, psoriatic arthritis; RF, rheumatoid factor.
*Adapted from Karmacharya, et al.¹

The ClASsification of Psoriatic ARthritis (CASPAR) criteria was developed in 2006, which provided some uniformity in defining PsA, though not all studies use this system as it requires a physical examination of the patient. Studies that used the International Classification of Diseases (ICD) codes found the lowest prevalence of PsA, whereas studies that used self-reported PsA diagnoses reported the highest prevalence.

Most studies of prevalence trends of PsA have shown an increase in recent years. No clear sex predominance has been identified, with studies from different countries finding opposing results. For example, a higher prevalence in males was recorded in Norway and Argentina, whereas in the Czech Republic and Denmark, a greater prevalence of PsA was noted in females.

PsA prevalence and incidence in patients with psoriasis

In patients with psoriasis there is also variability in the prevalence of PsA recorded by different studies. One study reported a prevalence of PsA in patients with psoriasis of 19.7% (95% confidence interval, 18.5−20.9%), with adults having a much higher prevalence than children/teenagers at 21.6% vs 3.3%, respectively. In addition, a higher prevalence of PsA was noted in patients with moderate to severe (24.6%) compared with mild (15.8%) psoriasis.

The prevalence of PsA in patients with psoriasis has been shown to be variable between continents:

• Asia, 14.0%
• Africa, 15.5%
• North America, 19.5%
• South America, 21.5%
• Europe, 22.7%

The incidence of PsA among patients with psoriasis is also varied, ranging from 1.7% to 7.4% (Figure 2).

Figure 2. Incidence of PsA among patients with psoriasis*

CASPAR, Classification of Psoriatic Arthritis; CI, confidence interval; M/F, male to female; NR, not reported; PsA, psoriatic arthritis.
*Adapted from Karmacharya, et al.¹

Mortality

Evidence regarding the impact of PsA on mortality is conflicting, with the standardized mortality rate (SMR) varying from 0.05 to 98.5 (Figure 3). Older studies may show a higher SMR than more recent ones.

Figure 3. Mortality of PsA: overall and cause-specific*

aHR, adjusted hazard ratio; CASPAR, Classification of Psoriatic Arthritis; CHF, congestive heart failure; CI, confidence interval; CVA, cerebrovascular accident; ESSG, European Spondylarthropathy Study Group; HR, hazard ratio; ICD, International Classification of Diseases; MI, myocardial infarction; NR, not recorded; PsA, psoriatic arthritis; RR, relative risk; SHR, standardized hazard ratio; SMR, standardized mortality rate; TB, tuberculosis.
*Adapted from Karmacharya, et al.¹

A prospective study from the University of Toronto has demonstrated decreased mortality risk over time across almost four decades of follow-up:

• from 1978 to 1986, the SMR was 1.89;
• from 1987 to 1995, the SMR was 1.83;
• and from 1996 to 2004, the SMR was 1.21.

A more recent study from 1978 to 2017 showed no increase in overall mortality rate, with an SMR of 0.92 (95% confidence interval, 0.81−1.05). While evidence is currently contradictory regarding the impact of PsA on cardiovascular mortality, some studies have shown an increase in risk. Occasionally, cause-specific mortality for respiratory diseases has also been linked to PsA; however, again the data are conflicting.

Conclusion

While an increasing trend in PsA prevalence has been seen in recent years, PsA remains underdiagnosed. The development of PsA is complex and multifactorial. Overall mortality does not appear to be increased in patients with PsA; however, there is an increase in certain cause-specific mortality groups such as cardiovascular comorbidities.