A 31-year-old woman presented with asymptomatic, erythematous, cutaneous lesions on her back. The rash began 2 months before and was neither pruritic nor painful. She denied arthralgia, fever, or other symptoms. The patient had a long history of arthritis and back pain. On physical examination, there was a well-defined, brown, erythematous, and reticular patch that occupied the entire lower back. Complete blood count, routine urinalysis results, liver and renal function, serum glucose and electrolyte levels, and erythrocyte sedimentation rate were all within normal limits.
The most likely diagnosis is
Acanthosis nigricans
Livedo reticularis
Erythema ab igne
Systemic lupus erythematosus
Livedo vasculitis
Answer on page 669