What is the cause of hair loss and elevated eosinophils in an adult patient?

Hair Loss and Elevated Eosinophils: Diagnostic Approach

Hair loss with elevated eosinophils most commonly indicates hypereosinophilic syndrome (HES) when other causes are excluded, requiring urgent evaluation for end-organ damage and immediate corticosteroid therapy if confirmed. 1

Initial Risk Stratification

The absolute eosinophil count (AEC) determines urgency and diagnostic approach:

• Mild eosinophilia (0.5-1.5 × 10⁹/L): Most commonly caused by allergic disorders or medications in non-endemic areas, but helminth infections account for 19-80% in returning travelers 2
• Moderate-to-severe eosinophilia (≥1.5 × 10⁹/L): Requires hematology referral if persisting >3 months after infectious causes excluded 2
• Hypereosinophilia (≥1.5 × 10⁹/L): Demands immediate evaluation for end-organ damage regardless of symptoms 3, 2

Critical Red Flags Requiring Urgent Assessment

Evaluate immediately for life-threatening complications:

• Cardiac involvement: Chest pain, dyspnea, heart failure symptoms, or arrhythmias suggest endomyocardial thrombosis/fibrosis, particularly with neoplastic HES variants 3, 2
• Neurological symptoms: Altered mental status, focal deficits, or peripheral neuropathy indicate CNS/spinal cord involvement 3, 2
• Pulmonary involvement: Persistent cough, wheezing, or infiltrates on imaging 3, 2

Systematic Diagnostic Workup

Step 1: Exclude Secondary Causes (Most Common)

Allergic disorders account for ~80% of secondary eosinophilia 3:

• Atopic dermatitis, allergic rhinitis, asthma, drug reactions
• Note: Alopecia areata (AA) patients with concurrent eosinophilia have 3.70 times higher odds of severe hair loss and increased nail abnormalities compared to AA without eosinophilia 4

Parasitic infections (second most common cause) 3:

• Obtain detailed travel history: fresh water exposure in Africa/tropical regions, raw/undercooked meat consumption 2
• Order 3 separate concentrated stool specimens for ova/parasites 2
• Send Strongyloides and Schistosoma serology based on exposure history 2
• Critical: Strongyloides can persist lifelong and cause fatal hyperinfection in immunocompromised patients 2

Medication reactions: Review all current and recent medications 5

Step 2: Assess for End-Organ Damage

Mandatory cardiac evaluation for AEC ≥1.5 × 10⁹/L 2:

• ECG, cardiac troponin, NT-proBNP
• Echocardiography if troponin elevated or cardiac symptoms present
• Cardiac MRI to distinguish eosinophilic cardiac disease from other etiologies

Dermatologic assessment (directly relevant to hair loss):

• Deep skin biopsy including fascia to document eosinophilic infiltration 2
• Scalp biopsy showing dense perifollicular eosinophilic infiltration confirms HES-related alopecia 1

Additional organ systems 3, 2:

• Pulmonary: Chest X-ray, pulmonary function tests if respiratory symptoms
• GI: Endoscopy with biopsies if dysphagia, diarrhea, or abdominal pain
• Neurologic: EMG and nerve biopsy if peripheral neuropathy suspected

Step 3: Rule Out Myeloproliferative/Lymphocytic Variants

If secondary causes excluded and hypereosinophilia persists 3:

• Bone marrow biopsy with cytogenetics
• Test for FIP1L1-PDGFRA fusion gene (responds to imatinib)
• Flow cytometry to exclude lymphocytic variant HES
• Serum tryptase and vitamin B12 (elevated in myeloproliferative variants)

Treatment Algorithm

For Confirmed Hypereosinophilic Syndrome with Hair Loss

Immediate corticosteroid therapy is first-line 1, 6:

• Oral prednisone 1 mg/kg/day initially
• Effective for reducing both hair loss and blood eosinophilia
• Critical caveat: Relapse is common after discontinuation, requiring long-term maintenance 1

For Parasitic Infections

Empiric treatment while awaiting results in endemic-exposed patients 2:

• Ivermectin 200 μg/kg daily for 2 days (Strongyloides)
• Albendazole 400 mg twice daily for 3 days (Ascaris, hookworm)
• Praziquantel 40 mg/kg single dose for Schistosomiasis

Critical warning for Loa loa: Do NOT use diethylcarbamazine if microfilariae seen on blood film—may cause fatal encephalopathy; use corticosteroids with albendazole first 2

For Myeloproliferative Variants

Imatinib 100-400 mg daily for FIP1L1-PDGFRA-positive cases 3

Common Pitfalls to Avoid

• Do not assume allergy alone explains hypereosinophilia (≥1.5 × 10⁹/L)—this level is rarely if ever caused by allergy and demands full workup 5, 6
• Do not rely on symptoms alone to assess organ damage—cardiac involvement can be subclinical initially 2
• Do not assume normal eosinophil count excludes parasites—many helminth-infected patients have normal counts 2
• Do not delay cardiac evaluation in moderate-to-severe eosinophilia—endomyocardial fibrosis can develop rapidly 3, 2
• Do not start corticosteroids before excluding Strongyloides in at-risk patients—can precipitate fatal hyperinfection 2

Prognosis and Monitoring

For HES-related diffuse alopecia with massive perifollicular eosinophils 1:

• Corticosteroids effectively reduce hair loss and eosinophilia
• Immediate relapse typical after treatment cessation
• Long-term maintenance therapy required
• Regular monitoring of AEC and organ function essential