PRESENTING FEATURES: An 85-year-old black woman presented to the Osler Medical Service complaining of a pruritic, erythematous scaly rash that was on her right thigh and abdomen and that had been worsening over the prior 3 months. She also complained of increasing fatigue, decreased exercise tolerance, and a 5-lbs weight loss. There was no orthopnea, paroxysmal nocturnal dyspnea, fevers, chills, or night sweats. She denied recent travel and exposures to or contact with ill people. Her past medical history was unremarkable. There was no history of eczema, atopy, or dermatologic conditions. Her only medication was a baby aspirin taken daily.

On physical examination, she was afebrile, her blood pressure was 110/72 mm Hg, and her pulse was 82 beats per minute with a room air oxygen saturation 98%. She was mildly obese but in no apparent distress. She had 1-cm anterior cervical lymphadenopathy bilaterally and a 1-cm left axillary lymph node. Cardiovascular and chest examination was unremarkable. Her abdomen was soft and nontender, with a faint, erythematous rash that was mildly scaly but nontender in her abdominal skin fold. Her right thigh showed a large erythematous area, approximately 15 × 20 cm, which was scaly with multiple areas of discoloration (Figure 1). There was no palpable mass. She had slight edema in her right leg. Her left thigh was normal. Neurologic examination was nonfocal.

Laboratory studies were notable for a white blood cell count of 17,000 cells/μL, with a differential of 46% lymphocytes. The absolute lymphocyte count was 8000 cells/μL. Hematocrit was 28%. Platelet count was normal. A comprehensive metabolic panel was normal. A peripheral blood smear (Figure 2) showed numerous atypical lymphocytes with cerebriform nuclei. Peripheral blood flow cytometry showed the presence of a clonal population of T cells that expressed CD4 and CD5 but showed a loss of CD7.

What is the diagnosis?