Tropical Pulmonary Eosinophilia (Occult Filariasis)

Epidemiology

  • Most common in Southeast Asia, India, South Pacific > Africa, South America (but cases have occurred in North American and European visitors to endemic areas
    • Requires exposure in endemic area for at least a few months
  • Age: usually occurs in 20-40 y/o
  • Sex: 80% of cases are males
  • Race: Indians are most susceptible
  • Possible relationship to Tropical Myocardial Fibrosis (unclear though)

Etiology

  • Wuchereria bancrofti (filiarial nematode, roundworm): mosquito-borne parasite that infests lymphatics (larvae mate in lymphatics and lymph nodes: shedding microfilariae to complete the life cycle)
    • Man is the only reservoir host
  • Brugia Malayi/Brugia Timori (filarial nematode, roundworm): mosquito-borne parasite that infests lymphatics
    • Occurs in human and animal hosts
  • Ancylostoma Duodenale: less common cause
  • Strongyloides Stercoralis: less common
  • Toxocara Canis: less common cause

Physiology

  • Transmission: mosquitoes transmit infected larvae into humans
  • Disease Course: larvae migrate within human lymphatics and get trapped in pulmonary microvasculature -> hypersensitivity/allergic reaction to filariae with lung injury
    • Early: histiocytic alveolitis and interstitial infiltration
    • Later: eosinophilic alveolitis
    • Late: granulomatous reaction and fibrosis (may cause pulmonary HTN when ILD is advanced)

Diagnosis

  • CBC: eosinophilia (usually 3,000-60,000: higher than that seen in Simple Pulmonary Eosinophilia)
  • Sputum GS/Cult+Sens: viscous with eosinophils
  • PFT’s: restriction (seen in all stages of disease)/obstruction seen in 25-30% of cases (typically early in course, in first month of disease)
  • FOB: eosinophilic alveolitis
  • CXR/Chest CT patterns:
    • 1-3 mm nodular interstitial infiltrates: mid and lower-lung zone predominance/nodules may cavitate
    • Diffuse miliary pattern: may be seen
    • Bronchopneumonia pattern: may be seen
    • Interstitial fibrosis: seen late
    • Pleural effusion (rare):
    • Normal CXR: in some cases
    • PTX (uncommon)
  • Serum /IgE: markedly elevated (usually >5,000 ng/mL)
  • Antifilarial Ab (against Dirofilaria Immitis antigen, etc.): elevated (diagnosticaly useful but may have lower titer elevation in helminthic infections, due to cross-reactivity)
  • ESR: may be elevated in advanced disease
  • Blood C/S and exam: negative
  • EKG: may be abnormal
  • Echo: may show pericardial effusion in some cases
  • Liver, Lymph node, or Lung Bx (rarely necessary for diagnosis): demonstrate filaria (but speciation is usually difficult)

Clinical

Lung Involvement

  • Cough (90%): may be nocturnal
    • Mucoid sputum (55%)
  • Paroxysmal Cough with Dyspnea (70%):
  • Exertional Dyspnea (45%):
  • Wheeze (28%):
  • Chest pain:
  • Wheezing/Rales, or Diffuse Rhonchi (20% of cases have normal lung exam) (see [[Obstructive Lung Disease]])

Constitutional

  • Weight Loss (52%):
  • Fatigue (75%):
  • Anorexia (42%):
  • Fever (25%):
  • Lymphadenopathy/Hepatosplenomegaly: seen mainly in children

Requirements for Diagnosis of Tropical Pulmonary Eosinophilia

[Respiration 1996: 63: 55-58; Respir Med 1998: 92: 1-3]

  • Residence in an Endemic Filarial Region
  • Insidious Onset and Prolonged Duration of Symptoms for >4 Wks
  • Nocturnal Paroxysmal Cough and Wheezing
  • Striking Peripheral Eosinophilia
  • Markedly Elevated IgE Levels
  • Elevated Filiarial Ab Titer

Treatment

  • Diethylcarbamazine (6 mg/kg/day -> usually 150 mg TID x 3 weeks): drug of choice
    • Symptoms usually improve within days (residual radiographic and PFT changes, BAL eosinophilia, and mild symptoms may persist for weeks-years after therapy)
    • Response to Trial is a diagnostic maneuver
    • Relapse (may occur): responds to repeat treatment
    • Delayed Therapy: may have poor clinical response with pulmonary fibrosis
    • SE: hypotension and urticaria/allergic Mazzotti’s reaction (edema and fever occurring within 16 hrs after first dose/due to lethal effect on coexistent Onchocerciasis)
    • Also has Anti-Helminthic Activity: may produce some response in helminthic infection
  • Mebendazole with Levamisole: may be used when allergic to diethylcarabamazine
  • Ivermectin: has not been evaluated
  • Treatment of Bronchospasm: usual therapies
    • Bronchodilators: as needed
    • Steroids: as needed

References

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