This is a previously healthy young woman who presented with subacute atraumatic pain and swelling of her right knee and left foot. The right knee was erythematous and warm with an associated joint effusion that contained 15K WBC/μL but no organisms or crystals. She was taken for a washout of the knee for presumed septic arthritis. Later, physical examination revealed well-demarcated erythematous plaques involving the posterior neck and ear, as well as the oil drop sign on one of her fingernails, consistent with psoriatic arthritis.
This patient also has an oil drop sign.
