Psoriatic arthritis (PsA) is a chronic (long-term) disease typically characterized by inflammation of the skin and joints. The skin inflammatory condition is psoriasis and the inflammatory arthritis is psoriatic arthritis.

These conditions develop because the immune system of the body mistakenly attacks your skin and joints.

Psoriatic arthritis (PsA) is classified into five different types and the type depends on the distribution of the affected joints in the body. Each type has its typical symptoms and varying degree of prevalence.

The peripheral joints are more commonly affected such as those of arms and hands, legs, and feet: elbows, wrists, ankles. The axial skeleton joints, namely the joints of the spine, hips, and shoulders are less commonly affected.

Types of psoriatic arthritis

Around the ’60s and ’70s, five clinical forms of psoriatic arthritis were distinguished by Moll and Wright. Their criteria for the classification were simple, which specified the presence of

  1. Psoriasis
  2. An inflammatory arthritis
  3. A negative test for rheumatoid arthritis

The location of your symptoms in the body depends on which type of PsA you have. Sometimes you may have more than one type. For example, you may have one type initially, which may develop into another type later on.

Since psoriasis and psoriatic arthritis often co-exist, symptoms of psoriasis often coexist with those of psoriatic arthritis.

Different types of psoriatic arthritis and their prevalence.

  • Distal interphalangeal joint-predominant arthritis – 10%
  • Symmetric polyarthritis-predominant arthritis -5% to 20%
  • Asymmetric oligoarthritis or monoarthritis – 70% to 80%
  • Axial disease predominant spondylitis and/or sacroiliitis – 5% to  20%
  • Arthritis mutilans – Less than 5%

Asymmetrical psoriatic arthritis

Also called asymmetric oligoarthritis, this type of PsA characteristically affects less than five joints of your body, small or big.

About 35 percent of people with psoriatic arthritis have this type. The symptoms are of mild nature and its typical feature is that the joints affected are on one side of the body, which are those of the knee, hip, toes, and fingers.

So, if your knee on one side of the body is affected, the knee on the other side stays healthy.

Symptoms and signs include

  • Red inflamed scaly patches of skin (if psoriasis is present, which it usually is)
  • Painful and limited movements of the joints such as flexion
  • Morning stiffness in the joints

Symmetric PsA

This type of psoriatic arthritis develops in joints on both sides of the body. It will affect the same pair of joints; for example right and left knees. This is the most common type and affects about half of the people who suffer from this type of arthritis. It usually affects five or more joints which, can be anywhere in the body.

A very close differential diagnosis is rheumatoid arthritis, which is also an autoimmune disease affecting joints on both sides of the body equally.

The differentiating factor is that the fingers in PsA swell more and look like sausages (Dactylitis) and usually accompanied by skin psoriasis symptoms.

Symptoms are of mild nature and similar to those of asymmetrical psoriatic arthritis such as morning stiffness and skin rashes.

Distal Psoriatic Arthritis

As the name “distal” suggests, this type of PsA affects the joints away from the body. These are the interphalangeal joints, those at the ends of the toes and fingers.

Since these joints are nearest to the nails, you will see spots, pitting on the nails, or the nail is detached from the nail bed. This type accounts for less than 10 % of the cases and though rare it can worsen if not treated.

The fingers get inflamed and stiff, which makes it difficult to perform simple day-to-day tasks such as opening a bottle or zipping your pants.

The junction of the ligaments and the tendons with the bones also get inflamed. This can erode the joints and lead to deformity and loss of function of the joints.

Spondylitis PsA

PsA of this kind involves the spine and the joints of the pelvis. It affects 20% of the people suffering from psoriatic arthritis. It can affect the entire spine from your neck to the lower back.

There is pain and stiffness from the neck to the lower back. Besides the spine, the joints of your hands, feet, legs, arms, and hips may also be affected. This makes movement of any kind such as bending forward or backward very painful.

There are periods of remission and flare-up when the symptoms subside and reappear.

Psoriatic arthritis mutilans

This is the most severe and deforming type of psoriatic arthritis, which can loss of bone tissue. It is rare, seen in only 5% of the people who suffer from PsA.

Psoriatic arthritis mutilans usually develops in the hands, though at times, it is seen in fingers, wrists, and feet.

Symptoms include almost loss of the affected joint movements. It is impossible to bend or straighten the finger. The joints involved shorten over time causing the skin over the joint to become loose.

Psoriatic arthritis mutilans is a progressive disease and the sooner it is diagnosed and treated can help to slow down the progression.

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