Types of Psoriatic Arthritis

There are different types of psoriatic arthritis.  Classification varies, depending on the source:

  • Asymmetric Oligoarticular PsA affects fewer than four joints, and (unlike RA) does not affect the same joint on both sides of the body.  This type of PsA is generally considered mild due to the small number of joints affected.  “Mild” is a comparative word that does not necessarily take into account the impact of the disease on a person’s life.  Approximately 70% of people with psoriatic arthritis have this type.
  • Symmetric Polyarticular PsA affects four or more joints, and (like RA) can affect the same joint on both sides of the body.  This type of PsA is more severe since more joints are involved.  Approximately 25% of people with psoriatic arthritis have this type.
  • DIP Predominant affects mainly the distal interphalangeal joints of the fingers and toes.  Inflammation of the DIPs is a clue that the autoimmune disease involved is PsA instead of RA.  Approximately 5% of people with psoriatic arthritis have this type.
  • Arthritis Mutilans, aka chronic absorptive arthritis, affects fewer than 5% of PsA and RA patients.  This type is severe and causes deformity.
  • Enthesitis is inflammation of the tendon/ligament insertion sites (where tendons/ligaments attach to bone). Over time, fibrosis or calcification can occur.
  • Spondylitis includes inflammation of the cervical spine (neck) and sacral spine (lower back), as well as hands, feet, hips, knees, elbows, and other joints as in RA and symmetric PsA.
  • Dactylitis affects fingers and toes, and indicates swelling of the entire digit.  This is in contrast to RA, wherein joints will swell, but not entire fingers/toes.

ClASsification criteria for Psoriatic ARthritis (CASPAR) requires inflammatory articular disease, but not necessarily visible swelling or symmetry.  Spine pain, enthesitis, or tendonitis are sufficient.  If that criteria is met, then at least three points from the following five categories qualify a person for a diagnosis of psoriatic arthritis:

  1. Psoriasis — either
    1. current psoriatic skin or scalp disease diagnosed by a rheumatologist or dermatologist (2 points), or
    2. personal history of psoriasis (1 point), or
    3. 1st degree (parent, child, sibling) or 2nd degree (grandparent, grandchild, aunt, uncle, nieces, nephews, half-siblings) blood relative with psoriasis (1 point)
  2. Psoriatic nails (1 point)
  3. Negative RF blood test (1 point)
  4. Dactylitis (swollen “sausage” fingers/toes)– current or history (1 point)
  5. New bone formation near joints visible on x-ray (1 point)

Psoriatic Arthritis – often misdiagnosed

Doctors know that over time, tendinitis and bursitis can lead to pain in the muscles surrounding an affected joint/tendon/bursa.  It’s just a consequence of long-term inflammation.

This pain can interfere with sleep.  That seems obvious, but it’s amazing how many people don’t realize there’s a connection.  If your shoulder hurts, even if you manage to fall asleep, every time you roll over on it, the pain can awaken you.  Likewise if the pain is in your hip.  In fact, regardless of pain’s cause, it’s not at all unusual for pain to lead to sleep loss.  To make matters worse, loss of sleep magnifies pain.

This is why it is so important for tendonitis and bursitis to be diagnosed quickly.  The diagnosis leads to treatment:  physical therapy & anti-inflammatories (and sometimes muscle relaxants).  If you get a good physical therapist and do your prescribed exercises religiously, the problem can usually be well-managed and the pain will go away.

Unfortunately, sometimes doctors miss a tendonitis/bursitis diagnosis.  If the patient had no injury causing the problem, the doctors might miss the diagnosis.

PainCycle

Undiagnosed tendonitis in both shoulders eventually leads to muscle aches in the upper back and both arms.  Undiagnosed tendonitis in both Achilles tendons leads to muscle aches in the lower legs.  Undiagnosed bursitis in the hips leads to muscles aches in the thighs.  At this point, many doctors give up and call it “fibromyalgia” (unexplained muscle aches in all four quadrants), and move on to patients they can help. This, despite the fact that a diagnosis of bursitis and/or tendonitis would perfectly explain all the symptoms1.

Or maybe it isn’t tendonitis/bursitis.  Maybe it’s vague back pain.  Maybe it comes and goes — flaring up for a while, then disappearing.  Maybe it’s not symmetric (only one shoulder/hip/knee instead of both).

All of these situations call for a closer investigation of family history for symptoms of psoriasis.  Note, however, that at least 15% of people with psoriatic arthritis do not have skin psoriasis.

The diagnosis of psoriatic arthritis (PsA) often is missed, partly because patients may present with inflammatory spinal pain, tendinitis, enthesitis, or dactylitis rather than a “true arthritis.”
Jaya Philipose, MD and Atul Deodhar, MD

Many doctors won’t make a PsA diagnosis without seeing visible evidence of psoriasis.  They might not realize the criteria for diagnosis.  ClASsification criteria for Psoriatic ARthritis (CASPAR) requires inflammatory articular disease.  Spine pain, enthesitis, or tendonitis are sufficient; visible swelling is not required; neither is symmetry.  If that criteria is met, then at least three points from the following five categories are sufficient for a diagnosis of psoriatic arthritis:

  1. Psoriasis — either
    1. current psoriatic skin or scalp disease diagnosed by a rheumatologist or dermatologist (2 points), or
    2. personal history of psoriasis (1 point), or
    3. 1st degree (parent, child, sibling) or 2nd degree (grandparent, grandchild, aunt, uncle, nieces, nephews, half-siblings) blood relative with psoriasis (1 point)
  2. Psoriatic nails (1 point)
  3. Negative RF blood test (1 point)
  4. Dactylitis (swollen “sausage” fingers/toes)– current or history (1 point)
  5. New bone formation near joints visible on x-ray (1 point)

Under this criteria:

  • a person with enthesitis, a negative RF test (1 pt), and mild scalp psoriasis (2 pt) should be diagnosed with PsA.
  • a person with mild inflammatory spine pain, a first or second-degree relative with psoriasis (1 pt), evidence of new bone formation on x-rays (1 pt), and negative RF (1 pt)  should be diagnosed with PsA
  • a person with tendinitis, psoriatic skin disease (2 pt), psoriatic nails (1 pt), and a positive RF (0 pt) meets the criteria for PsA.

Although doctors used to consider psoriatic arthritis as a sub-type of rheumatoid arthritis, that is no longer the case.  Psoriatic arthritis is a separate condition with distinct diagnostic criteria.

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1There is a reason that many “fibromyalgia” patients thrive with physical therapy.  They do not actually have unexplained muscle pain.  Their muscle pain is caused by tendonitis and bursitis.  Treating the tendonitis/bursitis cures the muscle pain.  This in turn makes it possible for the patient to get restful sleep.

Note this is not the only possibility for a “fibro” diagnosis.  Another common missed diagnosis is heart disease.  Cardiologists have been known to tell patients that they do not have fibro; all their symptoms are due to heart disease, and the symptoms resolve if the heart disease is well-treated.

RA or PsA: What’s the Difference?

Red-hot, swollen joints lead to excruciating pain.  Patients, writhing in agony, phone their doctors for help.  For the lucky, a quick diagnosis is made:  rheumatoid arthritis.  The luck is in the speedy diagnosis, not in the unfortunate diagnosis itself.

Often the diagnosis is unclear.  Doctors aren’t sure what the problem is, or even if there is a problem.  Alas, it’s not unusual for busy doctors to give hurting people in this situation the brush-off with, “It’s all in your head.”  If  your disease doesn’t match the pattern described in textbooks (atypical presentation), it’s hard for doctors to recognize.  Diagnosis of autoimmune disease can take years.

Even when a doctor determines that autoimmunity is the culprit, it might not be clear exactly which disease is causing the problem.  Many have very similar symptoms. Fortunately, arthritic diseases caused by a faulty immune system respond to similar medicines.  In order to get insurance to cover treatment, a diagnostic-label is sometimes affixed despite the uncertainty.  Over time, the uncertainty is forgotten and the tentative label takes on a life of its own.  Maybe it doesn’t matter.  After all, at least the patient gets treated.

Then again, maybe accurate diagnosis wherein different diseases are clearly distinguished would lead to better data about which medicines would be most likely to help a given patient.  It’s maddening to suffer through years of trial-and-error hoping to find effective treatment. When rheumatologists evaluate a new patient with autoimmune arthritis, one question is, “Is this rheumatoid arthritis, or is it psoriatic arthritis (or is it something else entirely)?”  Keys they look for are 1) nail involvement, and 2) skin psoriasis.  There is no nail involvement in RA.  In PsA, 80% of patients have nail symptoms such as ridges, grooves, and/or pitting.  Psoriatic finger/toenails can thicken instead of growing longer, sometimes even crumbling or falling off.  The problem with using nails as diagnostic criteria is that, according to the National Psoriasis Foundation, 20% of PsA patients do not have nail symptoms.  I propose that looking for ridged nails without asking about ridged nails is an exercise in futility, since people with unsightly nails might address the issue.  Furthermore, according to the American College of Rheumatology, “Psoriatic arthritis can occur in people without skin psoriasis, particularly in those who have relatives with psoriasis.”  In fact, in juveniles, up to half of PsA patients experience arthritis symptoms before there is any skin involvement.  Obviously we have a problem.

Dr. Irwin Lim, rheumatologist, writes:

Many patients labeled as having “Seronegative Rheumatoid Arthritis” or “Seronegative Inflammatory Arthritis” may have Psoriatic Arthritis.

In two short video clips, he explains more:

Not all patients with the diagnosis of psoriatic arthritis will have skin manifestations. Sometimes the diagnosis is made from a collection of other symptoms and signs, and a positive family history. Sometimes the rash actually occurs years after the development of psoriatic arthritis. So, it’s definitely possible to have psoriatic arthritis without the skin psoriasis.

Psoriatic arthritis can be very difficult to diagnose. It really does require the doctors to have a high index of suspicion. In patients who already have psoriasis affecting the skin or nails, the diagnosis is much easier because most people would think about it. But, sometimes, the symptoms can be quite vague. So many people have back pain, and it’s often explained away. In addition, joints aches and pains are common in the community, and sometimes the link with psoriatic arthritis is not put together. So, typically the diagnosis is made by an experienced physician taking into account the history, the examination, and the clinical context.

He is not alone in his views.  Doctors Jaya Philipose, MD and Atul Deodhar, MD write

The diagnosis of psoriatic arthritis (PsA) often is missed, partly because patients may present with inflammatory spinal pain, tendinitis, enthesitis, or dactylitis rather than a “true arthritis.”

It’s important to note that the rheumatologist is looking for clues at a single moment in time. In contrast, the patient knows a lifetime’s worth of history. If patients know the types of patterns that doctors are looking for, we can better provide the information that our doctors need to make an accurate diagnosis.

Usually doctors looking at family history are only interested in first-degree blood relatives:  parents, children, and full-siblings.  When considering psoriasis, though, doctors are also interested in second-degree relatives:  grandparents, grandchildren, half-siblings, aunts, uncles, nieces, and nephews.  Contact family members and ask.  Don’t just ask about psoriasis.  Ask about rashes and flakey skin.  Ask about severe dandruff — on the elbows and knees as well as on the scalp (not everyone is going to see a doctor for a diagnosis of those flakes).  See if  you can find a pattern.  Patterns can help your doctor make a diagnosis.

Following is a chart comparing some of the similarities and differences of RA & PsA:

PsAvsRA

For further reading: