Background: Psoriasis is a multifactorial disease of unknown origin.
Objective: Our purpose was to determine the frequency of skin disorders concomitantly seen in patients with psoriasis.
Methods: We analyzed data from more than 40,000 patients and calculated sex- and age-adjusted ratios of expected and observed incidence rates of associated disorders.
Results: The results demonstrate that, compared with age-matched control patients without psoriasis, cutaneous immune disorders such as allergic contact dermatitis, atopic dermatitis, and urticaria are underrepresented in patients with psoriasis. In contrast, certain systemic disorders such as diabetes, heart insufficiency, and obesity occur significantly more often in patients with psoriasis than in control subjects. Increased resistance to cutaneous bacterial infections was noted only in patients with early-onset psoriasis.
Conclusion: Our observations show that a distinct pattern of associated diseases exists in patients with psoriasis. Although systemic disorders such as obesity, diabetes, and heart disease may be related to dietary habits and nutritional status, the relative resistance to cutaneous infections together with decreased immune responsiveness suggest a genetically determined selection.