A 66-year-old man with extensive history of skin neoplasms including actinic keratosis, basal cell carcinoma, and low-stage melanoma presents to clinic with a persistent, pruritic, and irritated rash. He initially noticed redness on his head and face after he returned from a vacation in Florida, and it quickly spread throughout his torso, arms, and legs (Figure 1). He denies fevers, chills, fatigue, night sweats, or change in appetite or weight. He denies any new soaps, detergents, shampoos, or medications including over-the-counter supplements.

Positron emission tomography/computed tomography obtained four months after the first presentation demonstrated mild bilateral axillary and inguinal lymphadenopathy measuring up to 1.4 cm with maximal standardized uptake value of 2.9 cm. Complete blood counts are shown in the chart. Peripheral blood smear (Figure 2) showed circulating atypical cells. Additional flow cytometry was performed; the plots are depicted in Figure 3, with the population of interest marked in green. Although not shown, the cells of interest were negative for CD34 and TdT.

TestResultReference Range
White blood cell count 31.5 × 103/µL 3.5-11.0 × 103/µL 
Hemoglobin 11.8 g/dL 11.5-15.5 g/dL 
Platelet count 233 × 103/µL 150-450 × 103/µL 
Absolute neutrophil count 4.88 × 103/µL 1.12-6.72 × 103/µL 
Absolute lymphocyte count 2.99 × 103/µL 0.9-3.30 × 103/µL 
Manual Differential   
Neutrophils 16% 39-75% 
Lymphocytes 10% 16-47% 
Monocytes 2% 4 - 12% 
Eosinophils 3% 0-7% 
Basophils 1% 0-2% 
Myelocyte 1% 0% 
Other cells 67% 0% 
TestResultReference Range
White blood cell count 31.5 × 103/µL 3.5-11.0 × 103/µL 
Hemoglobin 11.8 g/dL 11.5-15.5 g/dL 
Platelet count 233 × 103/µL 150-450 × 103/µL 
Absolute neutrophil count 4.88 × 103/µL 1.12-6.72 × 103/µL 
Absolute lymphocyte count 2.99 × 103/µL 0.9-3.30 × 103/µL 
Manual Differential   
Neutrophils 16% 39-75% 
Lymphocytes 10% 16-47% 
Monocytes 2% 4 - 12% 
Eosinophils 3% 0-7% 
Basophils 1% 0-2% 
Myelocyte 1% 0% 
Other cells 67% 0% 

What is the diagnosis?

A. Follicular lymphoma

B. Pertussis related lymphocytosis

C. Sézary syndrome

D. T-lymphoblastic leukemia

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Competing Interests

Dr. Takeda and Dr. Venkataraman indicated no relevant conflicts of interest.