How should hyper‑eosinophilia be evaluated and managed in an adult patient with psoriasis who has an elevated eosinophil count?

Hypereosinophilia in Psoriasis: Evaluation and Management

In an adult patient with psoriasis and elevated eosinophil count, first exclude secondary causes (parasitic infections, drug reactions, atopic conditions) through targeted history and testing, then recognize that peripheral eosinophilia occurs in approximately 40-50% of severe psoriasis cases and does not require specific treatment unless absolute eosinophil count exceeds 1,500/mm³ for more than 3 months or end-organ damage is present. 1, 2, 3

Understanding Eosinophilia in Psoriasis Context

Prevalence and Clinical Significance:

• Peripheral blood eosinophilia is present in approximately 46% of systematically studied psoriasis cases, with no significant difference between having 1-5 eosinophils versus >5 eosinophils in tissue sections 1
• In severe psoriasis variants (erythrodermic and generalized pustular psoriasis), 41.7% of patients demonstrate peripheral blood eosinophilia, suggesting eosinophils play an active role in the pathogenesis of these severe forms 2
• The median absolute eosinophil count in psoriasis patients is approximately 259 cells/μL, which is elevated compared to controls but typically remains in the mild range 2

Algorithmic Approach to Evaluation

Step 1: Quantify the Eosinophilia Severity

Mild eosinophilia (0.5-1.5 × 10⁹/L or 500-1,500/mm³):

• Most commonly caused by allergic disorders, medications, or the psoriasis itself in non-endemic areas 3
• In patients with travel history to endemic regions, helminth infections account for 19-80% of cases 3

Moderate-to-severe eosinophilia (≥1.5 × 10⁹/L or ≥1,500/mm³):

• Requires hematology referral if persisting >3 months after infectious causes excluded or treated 3, 4
• Carries significant risk of end-organ damage and mortality 3

Step 2: Exclude Secondary Causes (Priority Order)

A. Medication-Induced Eosinophilia:

• Review all current medications, particularly biologics used for psoriasis treatment 5
• TNF-alpha inhibitors (including biosimilar adalimumab) can rarely cause marked eosinophilia, with eosinophil percentages rising from baseline 3.2% to as high as 19.9% 5
• Discontinue suspected offending agent if eosinophilia is marked (>10%) or symptomatic, as counts typically normalize after cessation 5
• Other common culprits include nitrofurantoin and various antibiotics 3

B. Parasitic Infections (Critical in Travel History):

• Obtain detailed travel history focusing on fresh water exposure in Africa/tropical regions, raw/undercooked meat consumption, and timing relative to eosinophilia onset 3
• Order three separate concentrated stool specimens for ova and parasites 3
• Send Strongyloides serology and culture immediately, as this parasite can persist lifelong and cause fatal hyperinfection syndrome in immunocompromised patients (including those on biologics for psoriasis) 3
• Send Schistosomiasis serology if fresh water exposure in endemic areas, as chronic infection can cause spinal cord compression or portal hypertension 3
• Critical warning: Do not use diethylcarbamazine if Loa loa microfilariae are seen on blood film, as it may cause fatal encephalopathy; use corticosteroids with albendazole first 3

C. Atopic/Allergic Conditions:

• 50-80% of patients with eosinophilia have concurrent atopic conditions (allergic rhinitis, atopic dermatitis, asthma) 3, 6
• Perform aeroallergen sensitivity testing (skin-prick or specific IgE assays) to identify trigger allergens 3
• Consider seasonal variation, as pollen season and aeroallergen exposure can elevate eosinophil counts 7

D. Eosinophilic Gastrointestinal Disorders:

• If dysphagia or food impaction present, perform upper endoscopy with minimum 6 biopsies (2-3 from proximal and 2-3 from distal esophagus) 7, 3
• Important caveat: Peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so normal blood counts do not exclude the diagnosis 3, 8
• Diagnosis requires ≥15 eosinophils per 0.3 mm² on esophageal biopsy 7, 8

Step 3: Assess for End-Organ Damage (If Eosinophils ≥1,500/mm³)

Cardiac evaluation (highest priority for morbidity/mortality):

• Obtain electrocardiogram, cardiac troponin, and NT-proBNP in all patients with hypereosinophilia 3
• Perform echocardiography if troponin elevated or symptoms present (chest pain, dyspnea, heart failure symptoms, arrhythmias) 3
• Consider cardiac MRI when elevated troponin or clinical features suggest cardiac injury 3

Pulmonary evaluation:

• Obtain chest X-ray to identify pulmonary infiltrates 3
• Perform pulmonary function tests if respiratory symptoms present (cough, wheezing, dyspnea) 3

Neurologic evaluation:

• Perform electromyography if sensory or motor deficits present to confirm eosinophil-induced peripheral neuropathy 3

Other systems:

• Deep skin biopsy including fascia if cutaneous involvement beyond psoriasis suspected 3
• Endoscopy with mucosal biopsy for gastrointestinal symptoms 3

Step 4: Determine if Hematologic Workup Needed

Indications for hematology referral:

• Absolute eosinophil count ≥1,500/mm³ persisting >3 months after secondary causes excluded 3, 4
• Any eosinophil count >5,000/mm³ 3
• Any evidence of end-organ damage 3
• Presence of fever, weight loss, or night sweats suggesting malignancy or systemic vasculitis 3

Hematologic evaluation includes:

• Morphologic review of blood and marrow 4, 9
• Standard cytogenetics and fluorescent in situ hybridization 4, 9
• Flow immunocytometry and T-cell clonality assessment 4, 9
• Testing for PDGFRA, PDGFRB, or FGFR1 rearrangements (critical because of exquisite responsiveness to imatinib) 4, 9

Management Strategy

For Mild Eosinophilia (<1,500/mm³) Without Organ Involvement:

Watch-and-wait approach with close follow-up is appropriate 4, 9

• Address identified secondary causes:

  • Discontinue offending medications if identified 5
  • Treat parasitic infections with appropriate antiparasitic therapy 3
  • Optimize control of atopic conditions (asthma, allergic rhinitis, eczema) 7

• Monitor eosinophil counts every 3-6 months to ensure stability 3

• Interpret changes in context of:

  • Patient's age 7
  • Adherence to aeroallergen avoidance 7
  • Pollen season 7
  • Control of comorbid allergic disease 7

For Moderate-to-Severe Eosinophilia (≥1,500/mm³) or End-Organ Damage:

Urgent hematology referral required 3, 4

• If PDGFRA or PDGFRB rearrangement identified: Imatinib is first-line therapy with exquisite responsiveness 4, 9

• If lymphocyte-variant hypereosinophilia or idiopathic HES: Corticosteroids are first-line therapy 4, 9

• For steroid-refractory cases: Consider hydroxyurea or interferon-alpha 4, 9

• For aggressive forms: Second-line cytotoxic chemotherapy or hematopoietic cell transplant may be required 4, 9

Critical Pitfalls to Avoid

• Do not assume eosinophilia is solely due to psoriasis without excluding parasitic infections, especially in patients with travel history, as many helminth-infected patients do not have eosinophilia initially 3

• Do not rely on peripheral eosinophil counts to diagnose eosinophilic esophagitis, as 50-90% of adults with EoE have normal blood counts; tissue biopsy is the gold standard 3, 8

• Do not wait for symptoms before investigating persistent moderate-to-severe eosinophilia, as end-organ damage can be subclinical initially 3

• Do not start corticosteroids before excluding Strongyloides infection in patients with travel history, as immunosuppression can trigger fatal hyperinfection syndrome 3

• Do not attribute eosinophilia to biologic therapy without considering other causes, as drug-induced eosinophilia is a diagnosis of exclusion 5

• Do not use diethylcarbamazine if Loa loa co-infection possible, as it may cause fatal encephalopathy 3

Monitoring During Psoriasis Treatment

For patients on biologic therapy:

• Baseline complete blood count with differential before initiating biologics 5
• Repeat CBC if symptoms develop (fever, rash, respiratory symptoms) 5
• If asymptomatic eosinophilia develops, continue monitoring every 4-8 weeks 5
• Discontinue biologic if eosinophil percentage exceeds 10% or absolute count exceeds 1,500/mm³ with symptoms or organ involvement 5, 3

Treatment response monitoring:

• Eosinophil counts can decrease 2- to 7-fold with corticosteroid treatment, with effects visible as early as 6 hours 6
• In eosinophilic esophagitis treated with topical steroids, 88% show decreased blood eosinophil counts 6