What is the appropriate diagnosis and treatment for a patient presenting with eosinophilia, lower limb pain, consolidation, and elevated IgE levels?

Tropical Pulmonary Eosinophilia (TPE) is the Most Likely Diagnosis

The clinical triad of eosinophilia, lower limb pain, pulmonary consolidation, and markedly elevated IgE levels is pathognomonic for Tropical Pulmonary Eosinophilia (TPE), a hypersensitivity reaction to lymphatic filarial worms (Wuchereria bancrofti and Brugia malayi), and treatment with diethylcarbamazine should be initiated promptly to prevent progression to pulmonary fibrosis. 1

Clinical Presentation and Diagnostic Features

TPE presents with a highly characteristic constellation of findings that distinguish it from other eosinophilic disorders:

Respiratory Manifestations

• Fever, dry cough, wheeze, and breathlessness are the hallmark respiratory symptoms 1
• Patients are frequently misdiagnosed initially as having asthma due to the prominent wheezing 1
• Chest radiograph may show interstitial shadowing, reticulonodular or miliary infiltrates, though 20% of cases have normal chest X-rays 1
• Pulmonary function tests reveal either obstructive deficits early in disease or restrictive deficits in later stages 1

Laboratory Findings

• Eosinophil count typically exceeds 3 × 10⁹/L, which is substantially higher than the mild eosinophilia seen in most allergic conditions 1
• IgE levels are markedly elevated, a key diagnostic feature 1
• Filaria serology is strongly positive 1
• Microfilariae are NOT detected on blood film microscopy, which distinguishes TPE from other filarial infections 1

Musculoskeletal Involvement

• Lower limb pain can occur as part of the systemic inflammatory response to filarial antigens 1
• This is distinct from the lymphatic damage and elephantiasis seen in chronic lymphatic filariasis 1

Epidemiology and Risk Factors

• TPE is more commonly seen in visitors to endemic regions than in long-term inhabitants, making travel history critical 1
• Endemic areas include regions where W. bancrofti and B. malayi are transmitted 1
• The condition represents a hypersensitivity reaction rather than direct parasitic invasion of the lungs 1

Treatment Protocol

Primary Treatment: Diethylcarbamazine (DEC)

Symptoms typically resolve rapidly following treatment with diethylcarbamazine 1

Dosing Regimen

• Start with 50 mg on day 1 1
• Increase gradually by day 4 to 200 mg three times daily 1
• Continue for 3 weeks total 1

Critical Pre-Treatment Screening

Before initiating DEC, onchocerciasis MUST be excluded to prevent severe complications including blindness 1:

• Obtain skin snips to rule out onchocerciasis 1
• Administer a test dose of 50 mg DEC and observe for Mazzotti reaction (pruritus and erythema) 1
• If onchocerciasis is present, pre-treat with ivermectin before giving full-dose DEC 1

Alternative Treatment Options

• Combination of ivermectin and albendazole may be used instead of DEC in areas where onchocerciasis is endemic 1

Adjunctive Corticosteroid Therapy

• Steroids may be used for treatment of ongoing alveolitis and pulmonary fibrosis 1
• Strongyloidiasis must be excluded before starting steroids to prevent hyperinfection syndrome 1

Clinical Management Considerations

Monitoring and Follow-Up

• Relapses occur in 20% of cases, necessitating re-treatment 1
• Follow-up eosinophil counts should be obtained after treatment to assess response 2
• Repeat chest imaging if respiratory symptoms persist 1

Prognosis and Complications

• If treatment is delayed or incomplete, pulmonary fibrosis may result, which is irreversible 1
• The condition rarely progresses to lymphatic damage when treated appropriately 1
• Early recognition and treatment prevent long-term morbidity 1

Differential Diagnosis to Exclude

While TPE is the most likely diagnosis, other conditions should be considered in the initial workup:

Parasitic Infections

• Strongyloidiasis can cause eosinophilia with pulmonary infiltrates (Löffler's syndrome) but typically has gastrointestinal symptoms 1
• Paragonimiasis presents with pleuritic chest pain and eosinophilic pleural effusions, with elevated IgE in >80% of cases 1
• Schistosomiasis (Katayama syndrome) can cause acute eosinophilia with pulmonary symptoms but typically includes abdominal pain and diarrhea 1

Non-Parasitic Causes

• Hypereosinophilic syndrome requires eosinophilia ≥1.5 × 10⁹/L for >3 months and is a diagnosis of exclusion 3
• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss) can present with asthma-like symptoms and eosinophilia but typically has vasculitic features 4

Diagnostic Algorithm

1. Obtain detailed travel history focusing on exposure to endemic filarial regions 5
2. Measure absolute eosinophil count and IgE levels 1
3. Perform chest radiograph to assess for pulmonary infiltrates 1
4. Send filaria serology (strongly positive in TPE) 1
5. Examine blood film for microfilariae (negative in TPE, distinguishing it from other filarial infections) 1
6. Screen for onchocerciasis before initiating DEC therapy 1
7. Exclude strongyloidiasis with stool microscopy and serology before considering steroids 1, 2

Key Pitfalls to Avoid

• Do not mistake TPE for asthma – the presence of marked eosinophilia and elevated IgE with pulmonary infiltrates should prompt consideration of TPE 1
• Never start DEC without excluding onchocerciasis – this can cause severe reactions including blindness 1
• Do not use steroids before excluding strongyloidiasis – this can precipitate fatal hyperinfection syndrome 1
• Do not assume normal chest X-ray excludes TPE – 20% of cases have normal radiographs 1
• Do not delay treatment – incomplete or delayed treatment can result in irreversible pulmonary fibrosis 1