19th January 2024

Differential diagnoses 

It can often be difficult to differentiate between psoriatic arthritis and other types of inflammatory joint disease. However, distinguishing features can include pattern of joint involvement, dactylitis, enthesitis and the absence of rheumatoid factor or anti-CCP antibodies.

• Rheumatoid arthritis (RA) – RA is an important differential diagnosis. It tends to present as a symmetric polyarthritis affecting small joints of the hands and feet. This pattern of disease can be observed in patients with psoriatic arthritis; however, these patients often have distal interphalangeal joint involvement. Dactylitis and sacroiliitis are not seen in RA, and rheumatoid factor and anti-CCP are usually positive. Hand x-rays of patients with RA would reveal osteopenia, joint space narrowing, erosions, and subluxation.
• Gout – gout usually presents with acutely swollen, warm and tender joints, and most commonly has either a monoarticular or oligoarticular pattern; however, can also affect several joints in the hands and feet, especially in the elderly. Synovial fluid examination would reveal negatively birefringent, needle-shaped crystals.
• Erosive osteoarthritis (OA) – OA often occurs in middle-aged women and affects distal and proximal interphalangeal joints of the fingers. X-rays of the hand will show characteristic changes such as osteophytes and joint space narrowing.
• Ankylosing spondylitis (AS) – some patients with psoriasis may also present with inflammatory spinal disease, which can be difficult to distinguish from AS.
• Enteric arthritis – patients with enteric arthritis would have a co-existing diagnosis of inflammatory bowel disease.
• Septic arthritis – patients with septic arthritis usually present with an acutely swollen, warm, and tender joint with systemic features such as fever. Synovial fluid culture would reveal the presence of underlying organisms.
• Reactive arthritis – reactive arthritis often presents with oligoarthritis, usually in weight-bearing joints and can also include dactylitis and enthesitis. However, there may often be a history of preceding gastrointestinal or genitourinary infection, and features such as conjunctivitis and urethritis may also be present. X-rays may show soft tissue swelling.
• Mycobacterial tenosynovitis – patients with mycobacterium tuberculosis and atypical mycobacteria may also present with dactylitis; however, synovial biopsy and culture would reveal the underlying organisms in these cases
• Sarcoid dactylitis – chronic sarcoidosis can also present with dactylitis, but patients will often have other features suggestive of underlying sarcoid, e.g., lymphadenopathy, respiratory symptoms. Chest x-ray may reveal hilar lymphadenopathy, and serum ACE levels may be raised.