Differentiation between psoriatic arthritis and rheumatoid arthritis: a biochemical and statistical analysis of fingernail amino acids.

The differentiation between psoriatic arthritis and rheumatoid arthritis can be clinically difficult if there is no manifest psoriasis of skin or nail. In order to clarify this diagnostic problem, the amino acid patterns in seventy-five psoriatic and non-psoriatic nails have been studied. Using gas--liquid chromatographic techniques and discriminant analysis, a high degree of differentiation (96%) has been established between the normal looking nails of patients with psoriatic arthritis and those with rheumatoid arthritis. This biochemical/statistical approach to the fingernail enhances diagnosis in difficult clinical problems, particularly where there are no overt manifestations of psoriasis.