Psoriatic arthritis (PsA) is an inflammatory form of arthritis linked to the skin condition psoriasis, though they are distinct diseases. PsA is caused by an overactive immune system that mistakenly attacks healthy tissue, primarily targeting the joints and the areas where tendons and ligaments connect to bone, leading to pain, stiffness, and swelling. While many people with PsA also have the characteristic scaly skin patches of psoriasis, the primary concern is the potential for permanent joint damage. Early diagnosis and treatment are important for preserving joint function and reducing the risk of associated health conditions.
The Relationship Between Psoriasis and Psoriatic Arthritis
It is a misconception that psoriatic arthritis cannot exist without the skin condition. While psoriasis appears first in the majority of cases (about 85%), it is possible to develop joint symptoms without any visible skin plaques. This presentation is formally referred to as Psoriatic Arthritis Sine Psoriasi (PsA without psoriasis).
In roughly 15% to 17% of patients, joint inflammation precedes the onset of skin lesions or the lesions never appear at all. This atypical presentation often leads to delayed diagnosis because the primary visual cue is missing. However, the link remains strong, as many people in this group have a first- or second-degree relative with psoriasis, suggesting a shared genetic predisposition.
The underlying cause for both the skin and joint disease is systemic inflammation. Sometimes, very mild or hidden psoriasis may be present in areas like the scalp, groin, or under the nails, making it easy to miss. Even without the skin component, the joint disease is aggressive and requires a focused treatment approach.
Recognizing Symptoms Without Skin Involvement
When skin plaques are absent, diagnosis relies on recognizing specific patterns of joint and soft tissue inflammation. One distinctive sign is dactylitis, which presents as a uniform, “sausage-like” swelling of an entire finger or toe. This swelling is caused by inflammation affecting all the small joints and tendons within the digit simultaneously.
Another unique manifestation is enthesitis, which is inflammation where tendons or ligaments attach directly to the bone. Common sites include the Achilles tendon or the plantar fascia on the sole of the foot, causing localized pain. Unlike Rheumatoid Arthritis, PsA often involves an asymmetrical pattern, affecting joints on one side of the body, or only a few joints in total (oligoarticular).
Nail changes are also a subtle physical sign even without skin plaques. These changes include nail pitting (tiny dents in the nail plate) or onycholysis (separation of the nail from the nail bed). Many people also experience chronic fatigue and stiffness that is worse in the morning or after periods of inactivity, often lasting more than thirty minutes.
How Doctors Confirm the Diagnosis
Diagnosing psoriatic arthritis when the skin is clear requires a methodical process of exclusion and confirmation, typically managed by a rheumatologist. Since no single test exists, the doctor takes a detailed patient history, focusing on any family history of psoriasis or PsA. This family link provides a crucial diagnostic clue when personal skin disease is absent.
Rheumatologists use specific classification tools, such as the Classification Criteria for Psoriatic Arthritis (CASPAR). The CASPAR criteria use a point system requiring established inflammatory joint disease and a score of at least three points from clinical and historical features. Features like a family history of psoriasis, nail dystrophy, dactylitis, and a negative test for Rheumatoid Factor all contribute points toward a diagnosis.
Blood tests help rule out other inflammatory arthritis forms, such as Rheumatoid Arthritis (RA) or Gout. A test for Rheumatoid Factor (RF) is typically negative in PsA, which helps distinguish it from RA. Markers of inflammation like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) may be elevated, indicating active systemic disease.
Imaging studies are essential for confirming characteristic joint changes. X-rays and Magnetic Resonance Imaging (MRI) can reveal specific damage patterns, such as joint erosion or the formation of new bone near the joints (juxta-articular new bone formation), which is distinctive of PsA. These findings, combined with the CASPAR criteria and a physical exam, allow for a definitive diagnosis.
Treatment Focus When Psoriasis Is Absent
Treatment for psoriatic arthritis without skin involvement focuses entirely on controlling joint inflammation and preventing irreversible damage. Since the joint disease can be aggressive, treatment often starts quickly to manage symptoms and preserve long-term joint function. The approach is stepped, depending on the severity of the disease.
For milder cases, nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce pain and swelling. If the disease is more active or involves multiple joints, doctors typically use Disease-Modifying Antirheumatic Drugs (DMARDs). Medications like methotrexate and leflunomide suppress the overactive immune response that drives inflammation.
For people with severe or rapidly progressing joint disease, biologic therapies are prescribed. These advanced treatments target specific immune system proteins, such as Tumor Necrosis Factor (TNF) inhibitors or Interleukin (IL)-17 inhibitors, to halt the inflammatory cascade. These systemic therapies effectively reduce joint swelling and prevent further bone erosion.
Physical therapy and occupational therapy play an important role in long-term management alongside medication. These therapies help maintain joint mobility, increase muscle strength, and teach strategies for performing daily tasks with less strain. The goal of this comprehensive treatment is to achieve remission, protecting the joints and allowing an active life.