Psoriatic arthritis (PsA) is a chronic inflammatory disease that primarily targets the joints and connective tissues, extending beyond the skin condition psoriasis. While often recognized for affecting peripheral joints like the hands and feet, PsA can also cause inflammation in the spine and pelvis, known as psoriatic spondyloarthritis. This spinal involvement results in inflammatory back pain (IBP), a distinct type of discomfort fundamentally different from common backaches.
The Hallmark Characteristics of Inflammatory Back Pain
The pain associated with psoriatic spondyloarthritis is a deep, persistent ache or burning sensation concentrated in the lower back and buttocks. Unlike a muscle strain, this discomfort tends to have a gradual, insidious onset, developing slowly over weeks or months. A defining feature of inflammatory back pain is its paradoxical response to movement and rest.
Periods of rest, particularly sleeping or sitting for long stretches, cause the stiffness and pain to worsen. Conversely, engaging in physical activity or light exercise often leads to a noticeable improvement in symptoms. This phenomenon, sometimes called the “gel phenomenon,” means stiffness and pain peak after waking up in the morning.
Morning stiffness is a telling symptom, frequently lasting 30 minutes or longer. The pain also commonly causes sleep disruption, often waking individuals in the second half of the night, sometimes around 4 a.m. This chronic pain lasts for more than three months, distinguishing it from acute, temporary back pain episodes.
Specific Areas of Spinal and Joint Involvement
The pain in psoriatic spondyloarthritis stems from inflammation in specific anatomical locations, not just the central spine. A frequent site of inflammation is the sacroiliac (SI) joints, which connect the lower spine to the pelvis (sacroiliitis). This inflammation often manifests as pain deep within the buttocks, sometimes alternating between the left and right side.
While the lower back (lumbar spine) is most commonly affected, PsA can also cause inflammation higher up in the spine, involving the cervical (neck) and thoracic (mid-back) regions. Inflammation also occurs at the entheses, the sites where tendons and ligaments attach directly to the bone. This enthesitis can cause pain away from the central spine, such as in the chest wall, hips, or the back of the heel.
Imaging of the spine may reveal changes in the vertebrae themselves, with new bone growth forming asymmetrical bridges between the spinal bones, especially in the cervical area.
Differentiating PsA Pain from Common Mechanical Back Pain
Differentiating inflammatory back pain and mechanical back pain (MBP), which results from injury or wear-and-tear, is important for diagnosis. Mechanical pain, such as from a muscle strain or herniated disc, typically begins suddenly, often linked to a specific movement or injury. Mechanical back pain usually worsens with activity and improves with rest, the direct opposite of the pattern seen in PsA.
Inflammatory pain often has an onset before the age of 40. Mechanical pain can occur at any age and is generally localized to a specific area of strain. A person with PsA-related back pain may also experience systemic symptoms absent in mechanical issues, such as unexplained fatigue, skin or nail psoriasis, or swelling in peripheral joints.
The stiffness in mechanical back pain is usually short-lived, resolving within a few minutes of movement. In contrast, prolonged morning stiffness lasting more than half an hour indicates an underlying inflammatory process. Mechanical pain rarely wakes a person from sleep, whereas inflammatory pain is a primary cause of nocturnal awakening.
Management Strategies for PsA Spondyloarthritis
The treatment approach for PsA-related back pain differs significantly from that for mechanical back pain because it must address the underlying systemic inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) are often used as an initial therapy to relieve symptoms and reduce inflammation. However, NSAIDs are typically used alone only for mild cases and short-term relief.
For more significant spinal involvement, treatment escalates to powerful medications that modify the disease process. Biologic disease-modifying antirheumatic drugs (DMARDs), such as TNF inhibitors, are important as they target the specific inflammatory pathways driving the condition and can slow or halt spinal damage. Other advanced therapies, including IL-17 and JAK inhibitors, may also be used, especially if skin disease is present.
Physical therapy and regular, specific exercise maintain spinal mobility and muscle strength. Because this condition is complex and requires specialized knowledge, anyone experiencing these symptoms should consult with a rheumatologist to ensure an accurate diagnosis and a tailored treatment plan.