Acute Monoarthritis Symptoms and Causes

Monoarthritis is defined as arthritis involving one joint at a time. There are several possible causes of monoarthritis or monoarticular arthritis as it is also called, including infection, nonspecific inflammatory conditions, crystal deposition, trauma, neoplasm, and immunologic conditions.

The onset of monoarthritis is often sudden and intense with fever, joint pain, and joint swelling. The presentation of such symptoms requires rapid diagnosis and treatment to prevent joint destruction. The diagnostician must utilize a patient's medical history, physical examination, x-rays, blood tests, and synovial fluid exam to determine the cause of the monoarticular symptoms. While monoarthritis is usually associated with an acute condition, it also can be the initial symptom of what develops into a polyarthritis or chronic type of arthritis. It also can be caused by a noninflammatory joint condition, periarticular condition (i.e., around the joint), bone disease, or soft tissue disease.  

Joint pain in the wrist.
Don Klumpp / The Image Bank / Getty Images

Initial Symptoms Offer Important Clues

Trauma, fracture, or a loose body is suspected when monoarthritis develops suddenly. Monoarthritis that develops more gradually, over one or two days, is usually associated with inflammation, infection, or crystal deposition. Pain that, at first, is unrecognized but worsens gradually over days to weeks, may be due to an indolent or asymptomatic infection, osteoarthritis, or tumor. Typically, if there is morning stiffness, as well as joint pain and restricted movement, an inflammatory type of arthritis is suspected. Pain that occurs in a periarticular region is usually related to a soft tissue disorder. If monoarthritis is chronic, usually it is related to the pre-existing joint disease. But, before monoarthritis is classified as chronic, the causes of acute monoarthritis must be considered and ruled out. Let's consider a few examples of conditions that may cause acute joint or periarticular pain, according to Kelley's Textbook of Rheumatology:

Common Acute Monoarthritis

Trauma or Internal Derangement

Acute Monoarthritis Associated With Eventual Polyarthritis

Monoarthritis Associated With Non-Inflammatory Disease

  • Osteoarthritis
  • Charcot joints
  • Storage diseases, such as Hemochromatosis (iron disorder)

Synovial Diseases

Acute Monoarthritis of Systemic Disease

Acute Monoarthritis of Bone Diseases

  • Paget's disease
  • Osteomyelitis
  • Metastatic disease
  • Pulmonary hypertrophic osteoarthropathy

Diagnostic Testing

Blood Tests

Blood tests can reveal important clues. Inflammatory, septic, or crystal-types of arthritis usually are associated with an elevated sedimentation rate, elevated CRP, and a high white blood count. Systemic disease involvement is often determined by blood tests that test the function of the kidneys, liver, bone, and muscle. Rheumatoid factor, anti-CCP, antinuclear antibody test, protein electrophoresis, Lyme disease serology, as well as a slew of other blood tests, may yield results that help formulate the diagnosis. 

Imaging Studies

Plain x-rays can reveal the presence of soft tissue swelling, calcium in the periarticular tissues, fracture, loose bodies, localized bone disease, and evidence of joint destruction. CT scans may be ordered when more detail is needed. MRI is the best imaging option when soft tissue disease is suspected. MRI also can assess the extent of inflammation and joint damage, even if asymptomatic. Arthrography and bone scans are also imaging options. Also, ultrasound is an increasingly common imaging modality used in the clinic to diagnose soft tissue and arthritic conditions.

Synovial Fluid Analysis

The synovial fluid examination is considered the most useful test for evaluating acute monoarthritis. Synovial fluid is analyzed for its color and degree of cloudiness. The white blood cell count is determined to distinguish between inflammatory and non-inflammatory causes. A synovial fluid white blood cell count that is greater than 2,000 WBC/mm3 is typically associated with an inflammatory condition. Synovial fluid with a white blood cell count that is less than 2,000 WBC/mm3 is typically non-inflammatory.

The synovial fluid should be cultured and a gram stain performed to look for the presence of bacteria microscopically. Uric acid or CPPD crystals can be observed, if present, using polarized light microscopy. Synovial fluid can also be tested for glucose, protein, and lactic dehydrogenase.

1 Source
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  1. Becker JA, Daily JP, Pohlgeers KM. Acute monoarthritis: diagnosis in adults. Am Fam Physician. 2016;94(10):810-816.

Additional Reading
  • Abraham S, Patel S. Monoarticular arthritis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-.

  • Acute Monoarthritis. Max Field. Kelley's Textbook of Rheumatology. Ninth edition. Page 577.

By Carol Eustice
Carol Eustice is a writer covering arthritis and chronic illness, who herself has been diagnosed with both rheumatoid arthritis and osteoarthritis.