Low back pain: Psoriatic arthritis often affects the sacroiliac joint, where the flared bones of the pelvis attach to the sacrum, the triangular bone at the base of the spine. Pain in the lower back is also a symptom of ankylosing spondylitis, a form of inflammatory arthritis that causes the vertebrae to fuse.

Nail changes: Nails may become pitted or infected-looking, or even lift from the nail bed entirely. This symptom, which is unique to psoriasis and psoriatic arthritis, actually helps doctors confirm a diagnosis.

Stiffness: Joints tend to be stiff either first thing in the morning or after a period of rest. This is another facet of PsA that makes it hard to properly diagnose; people with osteoarthritis often experience similar stiffness.

Fatigue: People with psoriatic arthritis often experience general feelings of fatigue. This symptom is a common feature of rheumatoid arthritis.

Reduced range of motion: The inability to move joints and limbs as freely as before is a sign of psoriatic arthritis – and most other forms of arthritis.

Conjunctivitis: Those with PsA may notice redness and pain in tissues surrounding the eyes.

Flares: Many people experience frequent periods of increased disease activity and symptoms, called flares, while others have only infrequent flares. This waxing and waning of symptoms is frequently seen with RA, as well.

Types of Psoriatic Arthritis

There are five types of psoriatic arthritis:

Symmetric: Accounting for about 50 percent of psoriatic arthritis cases, this type affects joints on both sides of the body at the same time. Symmetric psoriatic arthritis is similar to rheumatoid arthritis, causing joint pain and inflammation.

Asymmetric: Often mild, this type of PsA appears in 35 percent of people with the condition. It’s called asymmetric because it doesn’t appear in the same joints on both sides of the body.

Distal interphalangeal predominant: This type of psoriatic arthritis causes inflammation and stiffness near the ends of the fingers and toes, along with changes in toenails and fingernails such as pitting, white spots and even lifting from the nail bed.

Spondylitis: Pain and stiffness in the spine and neck are hallmarks of this form of PsA.

Arthritis mutilans: Though it’s considered the most severe form of PsA, arthritis mutilans affects only five percent of people who have the condition. It causes deformities in the small joints at the ends of the fingers and toes, and can dissolve them almost completely.