Erythroderma With Atypical Lymphocytes: Lymphoma vs Drug Eruption
A 68-year-old man presents with 3 weeks of progressive generalized erythema covering ~90% BSA, with scaling, palmoplantar keratoderma, and intense pruritus. He began allopurinol 5 weeks ago for asymptomatic hyperuricemia. Exam: diffuse erythroderma, ectropion, no mucosal erosions, no target lesions. Labs: WBC 14.2 with 18% atypical lymphocytes, LDH 480 U/L (upper normal 250), eosinophils 0.9 (absolute), ALC 4.8. Skin biopsy shows spongiosis with a perivascular lymphocytic infiltrate and scattered atypical cells; TCR gene rearrangement is reported as clonal. Blood flow cytometry is pending. He is hemodynamically stable but has 2+ edema and 4 kg weight gain.
1. Construct a differential and explain how you would weigh drug eruption versus cutaneous T-cell lymphoma given the clonal TCR result. What does clonality actually prove here?
Read the worked answer
Differential: (1) drug hypersensitivity/DRESS-spectrum reaction to allopurinol (timing ~5 weeks fits; eosinophilia, edema, weight gain, LDH elevation fit); (2) erythrodermic mycosis fungoides/Sézary syndrome; (3) erythrodermic psoriasis or pityriasis rubra pilaris; (4) other lymphoma (adult T-cell leukemia/lymphoma).
Key teaching point: TCR clonality is not synonymous with malignancy. Benign reactive dermatoses - including severe drug eruptions - can show a dominant clone on TCR gene rearrangement. Clonality is a supporting, not diagnostic, finding. Weight it against: (a) the temporal link to allopurinol; (b) peripheral eosinophilia and marked LDH without circulating Sézary cells yet; (c) histology showing spongiosis, which argues against MF (MF is typically epidermotropic with minimal spongiosis); (d) absence of longstanding patches/plaques.
Decisive next step is blood flow cytometry for Sézary cells and a repeat biopsy from a fresh, non-erythrodermic site rather than treating the clone as proof of lymphoma. Do not commit to a lymphoma diagnosis on clonality alone.
2. He is stable but erythrodermic with 4 kg fluid gain. Outline immediate management priorities and the specific risk you are guarding against over the next 48 hours.
Read the worked answer
Priorities:
- Stop allopurinol now and document as a suspected culprit; avoid structurally related agents (febuxostat caution).
- Assess for DRESS organ involvement: check ALT/AST, creatinine, urinalysis, and TSH (thyroid involvement can be delayed); baseline echocardiogram if any concern for myocarditis.
- Fluid/electrolyte and thermoregulation management: erythroderma causes high-output state, insensible losses, and hypothermia risk. Track daily weights, strict I/O, albumin, and electrolytes; the 4 kg gain suggests third-spacing/edema rather than pure overload - avoid aggressive diuresis that worsens intravascular depletion.
- Skin barrier care: emollients, low-potency topical steroid to body, monitor for secondary infection (Staph aureus, bacteremia).
- Symptom control: antihistamines for pruritus; avoid starting systemic corticosteroids before blood flow cytometry if lymphoma remains plausible, since steroids can suppress circulating Sézary cells and obscure the diagnosis.
The 48-hour risk to guard against is high-output cardiac failure and sepsis from barrier loss, not the rash itself.
3. Blood flow cytometry returns 12% Sézary cells (CD4+, CD7-negative). How does this change your diagnosis and immediate plan?
Read the worked answer
A circulating clonal CD4+ population with CD7 loss and ≥1000 Sézary cells/µL (or a significant clone) pushes the diagnosis strongly toward Sézary syndrome (erythroderma + circulating clonal T cells + lymphadenopathy). This is now a hematologic malignancy, not a drug eruption - though a drug can precipitate erythroderma in a patient with underlying disease.
Revised plan:
- Staging: full skin exam with biopsy of any lymph nodes, LDH (already elevated), and peripheral blood for the Sézary cell count/flow; imaging (CT/PET) for nodes. Document BSA and nodal status per ISCL/EORTC criteria.
- Do not treat as DRESS; discontinue allopurinol as a possible trigger but do not expect resolution.
- Refer to cutaneous lymphoma/hem-onc for systemic therapy (e.g., skin-directed therapy for early skin-limited disease vs. systemic agents such as mogamulizumab or extracorporeal photopheresis for Sézary syndrome).
- Reassess the original biopsy with the new context; request CD7, CD26, and CD4/CD8 stains if not done.
Lesson: the clonal TCR was a true positive, but the diagnosis required the combination of erythroderma, circulating atypical cells, and immunophenotype - not the clone alone.