Inflammatory arthritis is a common term for several conditions that manifest as joint pain, swelling, and stiffness with varying degrees of functional impairment. These diseases can be broadly categorized as:
Noninfectious and nonimmune-mediated inflammatory arthritis
In cases of pain and swelling in a single joint, acute infection is a relatively common cause - one that can result in rapid and irreversible damage. In contrast, the majority of patients with involvement of multiple joints tend to have disorders of chronic duration. The prognosis is good for those who remain unclassifiable, with nearly 50% of such patients undergoing remission requiring no pharmacologic therapy on follow-up at 1 year. A multinational collaborative study on undifferentiated peripheral inflammatory arthritis summarized the diagnostic approach to this problem quite succinctly.  
Joint inflammation is not the only cause of joint pain. In addition to inflammatory joint diseases, pain can also be due to joint damage (e.g., osteoarthritis, or trauma leading to a fracture or internal derangement), referred pain, or an altered pain threshold (as is seen in central sensitization syndromes such as fibromyalgia). Pain due to an intra-articular pathology needs to be differentiated from referred pain arising from adjacent soft tissues or juxta-articular bone. In the context of referred pain, the range of motion of the joint is usually unaffected, and joint motion does not aggravate pain, whereas palpation over a regional bursa, tendon, or ligament can elicit pain.
The classic signs of inflammation generally also apply to inflammatory joint disease:
Pain (aggravated by movement)
Limitation of range of motion.
It is usually not possible to detect all of the above features (especially swelling and erythema) in deep-seated joints such as the shoulders, hips, intervertebral joints, and sacroiliac joints.
Most causes of oligoarthritis (involving 2-4 joints) or polyarthritis (involving ≥5 joints) can also be causes of monoarthritis, because almost any arthritic condition can initially affect a single joint. The most important and serious condition that needs to be considered in the workup of an acute monoarthritis is septic (pyogenic) nongonococcal arthritis. If the diagnosis is missed and appropriate antimicrobial therapy is not instituted early, rapid destruction of articular cartilage can lead to irreversible joint damage.
Associate Professor of Medicine
Cleveland Clinic Lerner College of Medicine of Case Western Reserve University
Department of Rheumatologic and Immunologic Disease
Orthopedic and Rheumatologic Institute
SC declares that he has no competing interests.
Professor of Rheumatology
University of Cambridge
West Anglia CLRN
HG declares that he has no competing interests.
Chief of Rheumatology
Professor of Medicine
Tufts University School of Medicine
DLG declares that he has no competing interests.
Division of Orthopedic Surgery
University of Alabama
BAP declares that he has no competing interests.
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