Numbers of Incidence Stable in US Patients with Psoriatic Arthritis

Paras Karmacharya, MD (SPARTAN)

A recent study identified a stable incidence in the trend of patients with psoriatic arthritis (PsA) in a US patient population since 2000.

Investigators, led by Paras Karmacharya, MBBS, MS, of the Mayo Clinic College of Medicine, found their data contrasted previous years of study with findings of increasing incidence of PsA among their regional population.

The data was compiled from the population-based cohort of Olmsted County, Minnesota, a predominately white population. Compiled data previously identified patients who fulfilled PsA criteria during 1970 – 1999. The most recent study included incident PsA, as well as age- and sex-specific incidence rates and prevalence, adjusted to the 2010 US White population.

Investigators accessed comprehensive medical records for residents in Olmstead County seeking medical care through the Rochester Epidemiology Project (REP) to provide an update of PsA prevalence relevant to the REP 2015 census update.

The number of incident cases followed a Poisson distribution (95% CI) and mortality rates estimate using Kaplan-Meier methods, compared to the expected survival rates in Minnesota white population.

Identifications of the population found 484 Olmsted County residents with potential diagnoses of PsA. Another 164 patients fulfilled Classification of Psoriatic Arthritis (CASPAR) criteria between the date range while the remaining cases were excluded for not matching criteria.

The annual incidence of PsA per 100,000 population was 8.5 (95% CI, 5.9 – 9.4) in the data compiled from 2000 to 2017. The point prevalence of PsA as recently as 2015 was 181.8 per 100,000 (95% CI, 156.5 - 207.1).

Males had a higher rate with 9.3 (95% CI, 7.4 – 11.3) than females with 7.7 (95% CI, 5.9 – 9.4). Incidence rate data remained relatively stable during 2000 – 2017 with no increase in males.

Data showed the increase in females at 3% per year from 2000 to 2017, compared to a 4% annual rise in incidence from 1970 to 1999. The overall rate of incidence PsA was largest for 40 – 59-year-old patients.

Among the patients, there was a majority with asymmetric joint involvement (82%). Distal interphalangeal joint (DIP) involvement was seen in 32% patients.

Patients also had diagnoses of enthesopathy (30%), dactylitis (44%) and inflammatory back pain (11%) during or prior to the diagnosis of PsA.

A majority of patients (91%) had psoriasis present at diagnosis, while 45% had a family history of psoriasis and 4% had a personal history of psoriasis.

Geographic regions were also used in comparison for the PsA rates. Investigators wrote the study results for the United States were consistent with those reported in a recent meta-analysis showing 8.26 PsA cases per 100,000 people. The results are also similar to the incidence estimates of 6.0 - 8.0 per 100,000 from most European countries.

However, this study had numbers higher than the meta-analysis (133 per 100,000), with investigators believing early data and geographic location may have been the cause.

“The difference in incidence and prevalence estimates across different geographic regions could be due to different data collection periods, underdiagnoses (in Asia), or genetic and environmental differences,” investigators wrote.

Mortality rates from PsA was similar to general population, without a significant change over time. This data is consistent from population-based studies, including the 1970 – 1999 Olmsted Data and recent data from the United Kingdom in the Health Improvement Network, according to investigators.

Increased mortality risk data in other studies may be a result of selection bias finding more active or severe PsA.

“Similarly, higher prevalence of obesity, hyperlipidemia, and smoking, which are strong risk factors for PsA, could account for higher prevalence of PsA in North America,” investigators wrote.

The study, “The Epidemiology of Psoriatic Arthritis over 5 Decades: A Population-Based Study,” was published online in Arthritis & Rheumatology.