Psoriatic arthritis Classification & external resources
ICD-10	L40.5, M07.
ICD-9	696.0

Psoriatic arthritis (also arthropathic psoriasis or psoriatic arthropathy) is a type of inflammatory arthritis that affects around 5-7% (according to Oxford Handbook of Clinical Medicine) of people suffering from the chronic skin condition psoriasis. Psoriatic arthritis is said to be a seronegative spondyloarthropathy and therefore occurs more commonly in patients with tissue type HLA-B27. Treatment of psoriatic arthritis is similar to that of rheumatoid arthritis. More than 80% of patients with psoriatic arthritis will have psoriatic nail lesions characterised by pitting of the nails, or more extremely, loss of the nail itself (onycholysis).

Psoriatic arthritis can develop at any age, however on average it tends to appear about 10 years after the first signs of psoriasis. For the majority of people this is between the ages of 30 and 50, but it can also affect children. Men and women are equally affected by this condition. In about one in seven cases the arthritis symptoms may occur before any skin involvement.

As well as causing joint inflammation, psoriatic arthritis can cause tendinitis and a sausage-like swelling of the digits known as dactilytis. Radiology will give the appearance of "fluffy, new" bone.

Types of psoriatic arthritis

There are five main types of psoriatic arthritis:

• Symmetric: This type accounts for around 50% of cases, and affects joints on both sides of the body simultaneously. This type is most similar to Rheumatoid arthritis and is disabling in around 50% of all cases.

• Asymmetric: This type affects around 35% of patients and is generally mild. This type does not occur in the same joints on both sides of the body and usually only involves less than 3 joints.

• Arthritis mutilans (M07.1): Affects less than 5% of patients and is a severe, deforming and destructive arthritis. This condition can progress over months or years causing severe joint damage.

• Spondylitis (M07.2): This type is characterised by stiffness of the spine or neck, but can also affect the hands and feet, in a similar fashion to symmetric arthritis.

• Distal interphalangeal predominant (M07.0): This type of psoriatic arthritis is found in about 5% of patients, and is characterised by inflammation and stiffness in the joints nearest to the ends of the fingers and toes. Nail changes are often marked.

Treatments

The underlying process in psoriatic arthritis is inflammation, therefore treatments are directed at reducing and controlling inflammation. NSAIDs such as diclofenac and naproxen are usually the first line medication.

Other treatment options for this disease include joint injections with corticosteroids - this is only practical if a few joints are affected.

If acceptable control is not achieved using NSAIDs or joint injections then second line treatments with immunosuppressants such as methotrexate are added to the treatment regimen. An advantage of immunosuppressive treatment is that it also treats the psoriasis in addition to the arthropathy.

Recently, a new class of therapeutics developed using recombinant DNA technology called Tumor necrosis factor-alpha inhibitors have come available, for example, infliximab, etanercept, and adalimumab. These are becoming increasingly commonly used but are usually reserved for the most severe cases. As more is learned regarding the long-term safety of these biologic agents there is a trend toward earlier use to prevent irreversible joint destruction.