There are several reasons why it is a challenge to diagnose psoriatic arthritis, Dr. Eder says. Some of those reasons include the heterogeneity of the condition; that it can be mistaken for conditions like fibromyalgia, osteoarthritis and mechanical back pain; and that it can be difficult to differentiate it from other forms of arthritis.
Moreover, unlike with rheumatoid arthritis, or systemic lupus erythematosus, or systemic vasculitis, no autoimmune diagnostic markers exist that inform the diagnosis of psoriatic arthritis, Dr. Eder explains.
“There is no one particular test (that can be performed) to help physicians (diagnose psoriatic arthritis),” she says.
It is important to note that the severity of psoriasis is not correlated with the presence of psoriatic arthritis, Dr. Eder says.
“Patients may have psoriatic arthritis even though they do not have skin disease when I see them,” she says.
Factors that predict the development of psoriatic arthritis in patients with psoriasis include nail disease, obesity, family history of psoriatic arthritis, and positivity of certain HLA alleles such as HLA-B27.
With an earlier diagnosis of psoriatic arthritis, patients can then get more rapid access to treatments, in particular more novel therapies such as biologic agents, Dr. Eder says. Several biologic medications, including tumor necrosis factor antagonists, IL-23 and IL-17 blockers, and phosphodiesterase-4 inhibitors, are effective in treating psoriasis only and psoriasis with psoriatic arthritis, Dr. Eder says
In a Canadian context, wait times to see a rheumatologist contribute to the delay in diagnosis of psoriatic arthritis. There is a relative shortage of rheumatologists, particular in rural areas of Canada, leading to long wait times for seeing a rheumatologist and delays in diagnosis.
“There is a need to improve the system and develop models of care to improve early detection (of psoriatic arthritis),” Dr. Eder says. “We need to find a better way to triage patients (to improve the range of diagnosis of psoriatic arthritis).”
There is an economic cost to psoriatic arthritis, and that cost rises as a patient’s disease advances and his or her function deteriorates.