Distinct ecchymotic lesions are noted on the back of a 57-year-old Vietnamese woman who presents to the emergency department with progressive malaise, night sweats, fever, and a dry cough of 2 weeks' duration. For 2 months, she has been taking prednisone(Drug information on prednisone) (20 mg/d), which was prescribed by another physician for suspected autoimmune hepatitis.
The patient's breath sounds are coarse; no wheezing, egophony, or dullness to percussion is noted. A chest film shows bilateral diffuse, patchy interstitial infiltrates with small nodules. Pulmonary tuberculosis is suspected, and the patient is placed in isolation. Treatment for Pneumocystis carinii infection and community-acquired pneumonia is started. A few days later, sputum smears are positive for acid-fast bacilli.What do you suspect is responsible for the circular skin lesions?