The above conditions are more common in patients with psoriasis than in those without, but the most common comorbidity of psoriasis is psoriatic arthritis. About one third of people living with psoriasis also experience psoriatic arthritis.
In 2020, the American Academy of Dermatology and the National Psoriasis Foundation published guidelines on the treatment of psoriasis with special attention to comorbidities. In addition, the American College of Rheumatology/National Psoriasis Foundation published guidelines specifically on treatment of psoriatic arthritis.
No specific diagnostic tests are available for psoriatic arthritis. Diagnosis of the disease is instead based on clinical and radiologic criteria in a patient with psoriasis. Radiologic features can help to distinguish psoriatic arthritis from other causes of polyarthritis, such as rheumatoid arthritis. In its early stages, however, radiography can miss psoriatic arthritis because damage to the bone may not yet be apparent. In its later stages, psoriatic arthritis may not appear symmetrically, as does rheumatoid arthritis.
The most characteristic laboratory abnormalities in patients with psoriatic arthritis are elevations of the erythrocyte sedimentation rate and C-reactive protein level. The results from these laboratory tests help to track the activity of the disease by measuring inflammation.
Patients with psoriatic arthritis are typically seronegative for rheumatoid factor, although this marker is detected in 5%-9% of patients. RF testing is usually associated with a high false-positive rate; thus, RF-positive and RF-negative patients should receive the same treatment.
The American College of Rheumatology/National Psoriasis Foundation recommend the following treatment strategies for psoriatic arthritis:
A treat-to-target approach, aiming for minimal activity
Trying tumor necrosis factor inhibitor biologics as first-line therapy
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Cite this: William James. Skill Checkup: A 27-Year-Old Woman With Erythematous Plaques on Her Elbow, Thighs, and Scalp - Medscape - Dec 20, 2021.