The Reliability of Laboratory Testing in Diagnosing Psoriatic Arthritis: A Case Report

Psoriatic arthritis is an uncommon, chronic inflammatory disease. Laboratory testing for psoriatic arthritis, although necessary for a complete work-up, is generally nondiagnostic for most patients. We present a case of a 26-year-old woman with unilateral plantar forefoot pain and swelling that was diagnosed as psoriatic arthritis. The diagnosis was made without the benefit of skin manifestations or definitive laboratory results, other than those from laboratory tests performed for an initial evaluation of acute-phase reactants. Radiographs showed nonspecific subchondral bone changes at a few metatarsophalangeal joints of the involved foot that suggested an inflammatory arthropathy. This case illustrates that the absence of specific serum markers for psoriatic arthritis can make its diagnosis challenging, especially in the absence of dermatologic changes of psoriasis.