Helpful clues in the diagnosis of psoriatic arthritis include:
- psoriasis skin lesions (well-defined, red, scaling plaques with silvery scale)
- nail changes (pitting, lifting of the nail plate, yellow discoloration)
- asymmetric joint pain and swelling
- swollen fingers and toes (dactylitis)
- redness and swelling at end knuckles (DIPs) or middle knuckles (PIPs)
- enthesitis (inflammation and tenderness where a tendon attaches to the bone); Achilles tendon and heel are very common sites
- back pain
- joint stiffness in the morning
Medical History
Since most patients with psoriatic arthritis will initially have psoriasis lesions, a medical history and physical examination are both very important in diagnosing psoriatic arthritis. Your doctor might ask the questions in order to help establish a diagnosis of psoriatic arthritis.
Physical Examination
In a person presenting with swollen, tender joints, an examination of the skin for typical lesions of psoriasis and nail changes can indicate the possibility of psoriatic arthritis. In addition to the skin exam, your doctor may make other assessments, such as taking your blood pressure, and listening to and examining your heart, lungs, and abdomen.
Your doctor will need to carefully examine your joints to look for changes in the joints, and identify the number of joints Report Joint affected. Many dermatologists refer patients to a rheumatologist for detailed examination of the joints and further testing.
Your doctor will look at, feel, and move your joints to assess the problem, and determine both the number of joints and the extent to which they are affected. Clues that suggest psoriatic arthritis include:
- the presence of hot, red joints
- sausage-like fingers and toes (dactylitis)
- different joints on opposite sides of the body (asymmetrical) are affected
- distal interphalangeal (DIP) joints are affected
Warmth in a joint can indicate inflammation, which is found in psoriatic arthritis as well as several other types of arthritis. Swelling in a joint can be due to several causes, e.g., thickening of the lining in the joints (known as synovium) or bony overgrowth. Crepitus refers to the sensation of crunching or grinding in a joint, which you can feel if your hand is placed over the joint while it is in motion.
Your doctor might feel your joints to determine whether you have pain when pressure is applied. In addition, inflammation at those sites where the tendon inserts into the bone is characteristic of psoriatic arthritis.
Finally, your doctor might try to move your joints through a range of movement, to see if they are normal. Those with deformities from psoriatic arthritis could have a limited range of movement. Your doctor will also evaluate the ability and strength of your grip.
Laboratory and Blood Tests
There is no single laboratory test that diagnoses psoriatic arthritis. Certain laboratory tests are usually performed to determine if there could be another cause for the arthritis. There are two important blood tests, including the rheumatoid factor and the antinuclear antibody (ANA).
The first test was described earlier; the second test excludes the presence of systemic lupus erythematosus (lupus). Antinuclear antibody is found in about 95 percent of people with lupus, but rarely in psoriatic arthritis. Because lupus symptoms are similar to those of psoriatic arthritis, a negative antinuclear test can help rule out lupus.
Your doctor could also order other blood tests to monitor the progress of your disease, rather than for diagnostic purposes. For example, an erythrocyte sedimentation rate (ESR) is a nonspecific test that can reflect the degree of joint inflammation.
Another test is a complete blood count (CBC), which is exactly that - a count of all the cells of the blood: red blood cells, white blood cells, and platelets. Red blood cells are important (they carry oxygen from the lungs to the rest of the body), and their levels can be reduced in those with psoriatic arthritis or other types of inflammatory arthritis. A decrease in the level of red blood cells is called anemia.
Joint Aspiration
A joint aspiration involves using a syringe to take fluid from a swollen joint. Examining the fluid for white blood cells, infection, or crystals found in other causes of arthritis can be very important for establishing the correct diagnosis.
X-rays
X-rays are helpful in making a correct diagnosis of psoriatic arthritis, and in evaluating the extent and severity of the arthritis. Sometimes people with psoriatic arthritis have little or no joint pain, so joint destruction can go unnoticed. An X-ray can show specific changes that help distinguish psoriatic arthritis from other types of arthritis. In addition, an X-ray can determine the extent of the damage to the joints and provide a baseline with which to compare later X-rays.
The areas typically involved are the end and middle knuckle joints, the spine, the lower back at the base of the spine (sacroiliac joints), and at the site of tendon or ligament insertions to bone (entheses). if psoriasis is evident or psoriatic arthritis is suspected, X-rays of the hands, wrists, feet, and sacroiliac joints may be taken. Other areas can be X-rayed, depending on the patient's symptoms. To find out more, you can check out Psoriatic Arthritis Diagnostic.