Spondyloarthritis is a group of inflammatory diseases that cause arthritis, primarily impacting the spine and the sacroiliac joints that connect the pelvis and lower spine. Undifferentiated spondyloarthritis (USpA) is a diagnosis within this group. It is applied when a person shows clear signs of spondyloarthritis, but their symptoms do not meet the criteria for a defined condition like ankylosing spondylitis or psoriatic arthritis.
The term “undifferentiated” signifies the clinical picture is not fully formed or doesn’t fit a recognized category. A physician may diagnose USpA when symptoms are present but not distinct enough to classify further. For instance, a person may have heel pain and a swollen knee but lack the back pain or skin rashes of other types. This diagnosis allows treatment to begin while observing how the condition evolves.
Defining Characteristics and Symptoms
The most common indicator is inflammatory back pain, which improves with exercise but not with rest. Individuals often experience morning stiffness lasting more than 30 minutes and pain severe enough to wake them during the night, distinguishing it from mechanical back pain.
USpA also frequently involves peripheral arthritis, causing pain and swelling in large joints like the knees and ankles. This arthritis is often asymmetric, meaning it affects a joint on one side of the body but not the other.
A specific symptom is enthesitis, which is inflammation where tendons and ligaments attach to bone, causing pain at the back of the heel or sole of the foot. Another sign is dactylitis, where an entire finger or toe swells into a “sausage-like” shape due to inflammation.
Some people experience symptoms outside the joints, known as extra-articular manifestations. These can include uveitis (eye inflammation), psoriasis (a skin condition with itchy rashes), or intestinal inflammation leading to diarrhea. Not every person with USpA will have these additional symptoms.
The Diagnostic Process
Diagnosing USpA begins with a rheumatologist, who will discuss the patient’s symptoms and review their personal and family medical history for patterns consistent with spondyloarthritis.
A physical examination assesses the patient’s range of motion and identifies specific areas of pain or swelling. The physician checks for tenderness at entheses points, like the heels and chest, and looks for signs of arthritis in peripheral joints.
Blood tests for C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can indicate inflammation, though they are not always elevated. A test for the HLA-B27 gene is also common, as this marker is associated with spondyloarthritis, but having the gene is only a risk factor, not a confirmation of disease.
Imaging studies visualize the joints and spine. While X-rays may not show early changes, a magnetic resonance imaging (MRI) scan is more sensitive. An MRI can detect sacroiliitis (inflammation of the sacroiliac joints) long before damage is visible on an X-ray.
Treatment and Management Strategies
Managing USpA is tailored to an individual’s symptoms, involving medications and other therapies to reduce inflammation, manage pain, and maintain physical function. Treatment is adjusted over time based on the patient’s response and any changes in their condition.
The first line of treatment is nonsteroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, to alleviate pain and stiffness. If symptoms persist in peripheral joints, a doctor may prescribe a disease-modifying antirheumatic drug (DMARD) like sulfasalazine. For persistent disease, biologic medications like TNF inhibitors or IL-17 inhibitors may be used to target specific parts of the immune system.
Physical therapy and consistent exercise are important for maintaining flexibility, improving posture, and strengthening muscles. A physical therapist can design a personalized program. Lifestyle adjustments like maintaining a healthy weight to reduce joint stress and quitting smoking also play a part in management.
Prognosis and Disease Progression
The long-term outlook for individuals with USpA is variable. For some, the condition may remain mild and “undifferentiated” indefinitely, with symptoms that come and go but do not worsen significantly. Some individuals may even experience remission, where their symptoms resolve completely.
For others, the disease may progress, and the diagnosis might be reclassified to a specific type of spondyloarthritis. This could be ankylosing spondylitis if spinal symptoms become prominent or psoriatic arthritis if a skin rash develops. Those who test positive for the HLA-B27 genetic marker have a higher likelihood of their condition evolving into ankylosing spondylitis.
Because the course of USpA is unpredictable, regular monitoring by a rheumatologist is necessary. Follow-up appointments allow the doctor to track changes in symptoms or disease activity. This evaluation ensures the treatment plan can be adjusted to manage symptoms and maintain a good quality of life.