If a member of your family has psoriasis or psoriatic arthritis, there’s a chance you will, too. Up to 40 percent of patients with psoriatic arthritis have a positive family history of psoriatic disease.

If you already have psoriasis and you’re experiencing joint pain, you probably have psoriatic arthritis. About 30 percent of people with psoriasis will go on to develop psoriatic arthritis in their lifetime.

A blood test that detects your rheumatoid factor, or autoantibodies that attack healthy tissue, can help determine if it’s rheumatoid factor or psoriatic arthritis. About 80 percent of people with rheumatoid arthritis have a positive rheumatoid factor of 14 IU/ml or higher.

But a positive rheumatoid factor test isn’t conclusive. About 15 percent of the total population carries rheumatoid factor in their blood without ever developing rheumatoid arthritis. A positive rheumatoid factor can also indicate other diseases, including parasites, gout, or lupus.

About 50 percent of psoriatic arthritis patients experience joint pain symmetry, when pain in joints on the left side of the body also appears on the right side of the body. But joint pain symmetry isn’t definitive. People with psoriatic arthritis also experience joint pain asymmetry – i.e., a swollen joint in the right middle finger and spinal inflammation.

People with psoriatic arthritis tend to experience whole inflamed digits called dactylitis, colloquially known as sausage fingers. Despite the nickname, dactylitis also affects the toes.

People with rheumatoid arthritis will more often experience nodules, or firm lumps, atop swollen joints. People with psoriatic arthritis don’t often exhibit nodules atop swollen joints.

People with psoriatic arthritis also often experience nail symptoms including nail pitting, which are tiny pitted dots that can appear all over the nails. People with rheumatoid arthritis rarely experience nail pitting, so this is a strong indicator of psoriatic arthritis.

Researchers have discovered genetic markers that are specific to psoriatic arthritis and rheumatoid arthritis. For psoriatic arthritis, it’s HLA Cw6 and B27 or the interleukin 23 receptor, which is also present in people with irritable bowel syndrome and ankylosing spondylitis. For rheumatoid arthritis, it’s human leucocyte antigenDRB1.

Get a second opinion from another rheumatologist. The bright side: Treatment for psoriatic arthritis and rheumatoid arthritis is often the same. For either disease, your doctor may prescribe a non-steroidal anti-inflammatory drug such as Motrin, an immunosuppressant like methotrexate, or any number of biologics on the market.