Plant Thorn Arthritis (Plant Thorn Synovitis or Thorn Arthritis)

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

  • Medical Editor: Catherine Burt Driver, MD
    Catherine Burt Driver, MD

    Catherine Burt Driver, MD

    Catherine Burt Driver, MD, is board certified in internal medicine and rheumatology by the American Board of Internal Medicine. Dr. Driver is a member of the American College of Rheumatology. She currently is in active practice in the field of rheumatology in Mission Viejo, Calif., where she is a partner in Mission Internal Medical Group.

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What joints are typically involved in plant thorn arthritis?

Plant thorn arthritis typically affects only a single joint -- the joint that was pierced by the plant thorn. The most common joints affected by plant thorn arthritis are those that can be exposed to being stabbed by falling into or brushing up against plants with thorns. Joints that are commonly affected by plant thorn synovitis include the small joints of the hands (metacarpophalangeal joints, proximal interphalangeal joints), feet, elbows, knees, and ankles.

What are plant thorn arthritis symptoms and signs?

Plant thorn arthritis causes the involved joint to be

  • swollen,
  • slightly reddish,
  • stiff,
  • painful.

The joint loses its full range of motion and is often tender. These symptoms may be noticed only many days after the initial thorn puncture. It is not uncommon for the person affected by plant thorn arthritis to remove the thorn immediately after the puncture and then develop the arthritis many days or weeks later and not even recall that the joint had been punctured previously! This is because the original thorn has actually left behind small fragments of thorn vegetable matter that gradually cause the inflammation of plant thorn arthritis. This form of single joint arthritis (monoarthritis) then becomes chronic until appropriately treated.

How is plant thorn arthritis diagnosed?

Plant thorn arthritis is suspected in a patient who presents with a single joint that is inflamed after it has been punctured by a plant thorn. This is true even if the patient recalls removing the thorn, as described above, because the thorn can leave behind tiny fragments of thorn matter that leads to the chronic inflammation of plant thorn arthritis.

Removal of joint fluid (joint aspiration) is performed to rule out bacterial or fungal infection of the joint.

Ultimately, the diagnosis of plant thorn arthritis requires either detection of a piece of thorn within the joint by radiology testing or surgical removal of the thorn fragments and identification of the fragments microscopically in the laboratory. Sometimes tiny pieces of thorns can be visualized using magnetic resonance imaging (MRI scanning), high-resolution computerized tomography (HR-CAT scanning), or ultrasound imaging. Often, however, the residual thorn fragments are too small to be seen with these methods and are detected only when identified in tissue that is surgically removed from the joint.

The affected joint lining tissue (synovium) is examined in the pathology department using microscopes. The tissue forms a characteristic reaction, called a granulomatous reaction, within the synovium (granulomatous synovitis). The microscopic thorn fragments are easily identified using a polarized light microscope as they appear brilliantly shiny (birefringent) to the examining pathologist.

Pathology photo showing multinucleated giant cell granulomatous reaction (triangle point), synovial hyperplasia, fibrosis, and adjacent foreign vegetable matter (arrow with thorn fragments) with H&E stain.
Pathology photo showing multinucleated giant cell granulomatous reaction (triangle point), synovial hyperplasia, fibrosis, and adjacent foreign vegetable matter (arrow with thorn fragments) with hematoxylin and eosin stain (H&E stain). Kindly provided by Xiaohui (Sheila) Zhao, MD, PhD, of the Department of Pathology and Laboratory Medicine, University of California, Irvine Medical Center.
Pathology photo showing thorn material (blue and yellow birefringent material) visualized under polarized light microscopy.
Pathology photo showing thorn material (blue and yellow birefringent material) visualized under polarized light microscopy. Kindly provided by Xiaohui (Sheila) Zhao, MD, PhD, of Department of Pathology and Laboratory Medicine, University of California, Irvine Medical Center.
Medically Reviewed by a Doctor on 5/11/2015
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