Causes and Diagnosis of Polyarthritis

Why Arthritis in More the Four Joints Is Concerning

Arthritic hand indicative of polyarthritis
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Polyarthritis (also known as polyarticular arthritis) is defined as arthritis which affects five or more joints simultaneously. Polyarthritis is most often associated with autoimmune diseases and is considered worrisome as it tends to progress to other joints over time.

Causes

Polyarthritis is most often caused by an autoimmune disorder in which a person's immune system mistakenly attacks its own cells and tissues.

The causes of autoimmune disease are not well understood but are believed strongly associated with genetics, environment, and exposure to everything from radiation to toxins.

Because autoimmune diseases tend to trigger an all-body response, those involving the joints will usually not appear in isolation as they might with osteoarthritis (a.k.a. "wear-and-tear arthritis").

The autoimmune disorders most commonly associated with polyarthritis include:

Polyarthritis can also be triggered by certain so-called alphaviral infections including the chikungunya virus and Mayaro virus.

While we tend to associated polyarthritis with progressive, non-reversible disease, it can also occur as part of an acute illness such as rheumatic fever wherein the inflammation may be transient and migrate between multiple joints.

Diagnosis

While polyarthritis is most commonly associated with autoimmune disease, the term itself simply describes the number of joints involved and nothing more. As such, it can be used to describe any number of conditions, permanent or transient, in which more than four joints are affected.

To this end, the physician will typically begin an investigation by looking at the two most likely causes of polyarthritis: rheumatoid arthritis (RA) and osteoarthritis (OA).

There are several clues that can help differentiate between the conditions:

  • With OA, the symptoms will usually start on one side of the body and spread to the other. With RA, the symptom can develop haphazardly on both sides.
  • With OA, the symptoms tend to start with one joint and spread outward to involve other adjacent joints. With RA, the symptoms can develop on small or large joints with no apparent pattern.
  • OA symptoms tend to develop gradually. RA can strike fast and suddenly.
  • OA will usually not have systemic (all-body) symptoms. RA will typically be accompanied by persistent fatigue and a general feeling of unwellness.
  • With OA, the joints may ache and be tender but have little or no swelling. With RA, the joints will be painful, swollen, and stiff.

Depending on the suspected cause, X-rays, ultrasound, blood tests, and a joint fluid analysis (also known as arthrocentesis) may be ordered.

For RA specifically, two blood tests known as the rheumatoid factor test and the anti-cyclic citrullinated peptide (anti-CCP) antibody test can help confirm the diagnosis.

By contrast, there are no blood tests to confirm OS. The diagnosis is on the basis of the physical exam, imaging tests, and the evaluation of blood and joint fluids to exclude RA and all other causes.

Sources:

Ledingham, J. "Diagnosis and early management of inflammatory arthritis." BMJ. 2017; 358:j3248. DOI: 10.1136/bmj/j3248.

Pujalte, G. and Albano-Aluquin, S. "Differential Diagnosis of Polyarticular Arthritis." Am Fam Physician. 2015; 92(1):35-41.