Fever in Essential Thrombocythemia: Evaluation and Management
Fever in essential thrombocythemia (ET) is a recognized constitutional symptom that warrants evaluation for disease progression, hydroxyurea toxicity if on treatment, or concurrent infection—not a primary diagnostic feature requiring specific ET-directed therapy.
Understanding Fever in the Context of ET
Fever appears in ET guidelines specifically as:
- A constitutional symptom indicating possible disease progression to post-ET myelofibrosis, defined as unexplained fever >37.5°C 1
- A marker of hydroxyurea intolerance/toxicity when it occurs during treatment 1
- An incidental finding that may lead to ET diagnosis, as demonstrated in a recent case of polycythemia vera presenting with persistent low-grade fever 2
Algorithmic Approach to Fever in ET Patients
Step 1: Determine if the Patient is on Hydroxyurea
If YES: Consider hydroxyurea-related fever as a primary differential. The ESMO guidelines explicitly list "HU-related fever" as a criterion for hydroxyurea intolerance in ET 1. This is a diagnosis of exclusion but should prompt consideration of alternative cytoreductive therapy if other causes are ruled out.
If NO: Proceed to Step 2.
Step 2: Assess for Disease Progression to Myelofibrosis
Look for these specific additional criteria (need ≥2 total) 1:
- Anemia with hemoglobin decrease ≥2 g/dL from baseline
- Leukoerythroblastic blood picture on peripheral smear
- Increasing splenomegaly (≥5 cm increase from left costal margin or newly palpable)
- Other constitutional symptoms: >10% weight loss in 6 months, night sweats
- Elevated LDH
- Bone marrow fibrosis grade 2-3 on biopsy
If fever plus ≥2 of these criteria are present, suspect post-ET myelofibrosis and obtain bone marrow biopsy for definitive diagnosis.
Step 3: Evaluate for Infection
This is the most common cause of fever in any patient, including those with ET. Perform targeted infectious workup 3:
- Blood cultures (before any antibiotics)
- Urinalysis and urine culture
- Chest imaging if respiratory symptoms
- C-reactive protein and procalcitonin
- Site-specific cultures based on examination findings
The recent case report emphasizes that even persistent low-grade fever (<38°C) in myeloproliferative neoplasms may warrant FUO-like evaluation when routine investigations are negative 2.
Step 4: Consider Other Secondary Causes
Rule out:
- Inflammatory conditions (check inflammatory markers already obtained)
- Medication reactions beyond hydroxyurea
- Thrombotic complications (fever can accompany thrombosis)
Critical Pitfalls to Avoid
Do not assume fever is "just part of ET" in newly diagnosed patients. Constitutional symptoms including fever are criteria for disease progression, not typical presenting features of stable ET 1.
Do not continue hydroxyurea if fever persists without clear alternative cause. HU-related fever is an established toxicity requiring drug discontinuation 1.
Do not miss post-ET myelofibrosis. This transformation occurs in approximately 10% of patients at median 8.5 years from diagnosis and significantly changes prognosis and management 4.
Do not overlook infection. Despite the myeloproliferative nature of ET, patients remain susceptible to standard infections, and cytoreductive therapy may increase infection risk.
Management Based on Etiology
For HU-related fever: Discontinue hydroxyurea and consider alternative cytoreductive agents (interferon-alpha, anagrelide, or ruxolitinib in resistant cases).
For post-ET myelofibrosis: Transition to myelofibrosis-specific risk stratification and treatment algorithms, which may include JAK inhibitors or consideration for allogeneic stem cell transplantation in appropriate candidates 5.
For infection: Treat with appropriate antimicrobials based on culture results and clinical syndrome 3.
For isolated fever without identified cause: Consider empiric antipyretics while completing evaluation, but do not delay bone marrow biopsy if progression criteria are met.