2 INTRODUCTION HP known as extrinsic allergic alveolitis Granulomatous, interstitial, bronchiolar and alveolar-filling lung diseasesCaused by repeated exposure and subsequent sensitization to a variety of organic and chemical antigens.
5 PATHOGENESIS Immunology: Cell-mediated immunity Repeated inhalation of antigens → sensitization → immunology response(type III,IV) → influx of neutrophiles → shift T lymphocytes (~70%)(predominantly of CD8)(↓CD4/CD8 )BAL → activated T lymphocytesLung biopsy:Interstitial mononuclear cell infiltrationGranulomatous inflammatory responseAntibodies in HP are IgG class
6 PATHOGENESIS . . . Host factors: Exposure factors: Host susceptibility or resistance factors may influence individual responses to inhaled antigens.Non smokers > smokersNo association with HLAExposure factors:Ag concentrationDuration of exposureFrequency & intermittency of exposureParticle sizeUse of respiratory protectionFarmer's lung disease: winterBird breeder's lung: summer
7 CLINICAL FEATURES Acute HP: Fever ,chills ,myalgia ,cough , dyspnea (4-12 h after heavy exp. )Ph/E : basilar rales , peripheral leukocytosisRecurrent febrile episodes (most frequent presentation)
8 Subacute and chronic HP: CLINICAL FEATURES . . .Subacute and chronic HP:Temporal relationship between symptoms and exposure is difficult to elicit.Insidious onset of respiratory symptomsNon-specific systemic symptomsMalaise, fatigue, weight loss, cough, dyspnea, low grade feverPh/E: normal or basilar crackles & wheezingEnd-stage disease: cyanosis & right-sided HF
9 L/D ↑ Specific IgG ( no sensitive , no specific ) ↑ ESR & CRP ↑ IgM , IgA, IgG↑ ACE↑ ANA
10 PFTThere is no single characteristic pattern of pulmonary function abnormalities .Acute HP : restrictive patternSubacute and chronic HP : air way obstruction or mixed↓ DLCO (most sensitive physiologic test in early HP )Methacholine challenge test : increased non-specific bronchial hyper-reactivity
14 Airspace consolidation Only reported in acute HPBilateral ill-defined areas of consolidation
15 Subacute HP: bilateral alveolar and reticular pattern
16 Centrilobular nodules Round, poorly defined, less than 5 mm in diameterTypically centrilobularProfuse throughout the lung,but a middle to lower lung zone predominance.Most frequent HRCT finding in HPCentrilobular nodules + ground glass opacification are highly suggestive for HP.PFT : normal
17 Fibrosis Chronic HP (subacute HP) Irregular linear opacities Traction bronchiectasisHoneycombing
18 EmphysemaChronic HPEmphysema occurred more commonly than fibrosis in chronic farmer’s lung.
34 PROGNOSIS The clinical course of HP is variable Acute HP generally resolves without sequelaeBut progressive impairment may occur with recurrent attacks or with a single severe attack.Subacute or chronic forms of HP present with insidious symptomsMore subtle clinical abnormalitiesFrequently recognized later in the disease courseLong-term mortality rates for patients with chronic HP range from 1% to 10%.
35 Prognostic factors Age Duration of exposure after onset of symptoms Time of exposure prior to diagnosis
36 TREATMENT Cornerstone of therapy → removal from exposure Respirators are used when removal from exposure is impossible.Oxygen (hypoxemic patients)Airflow limitation:Inhaled steroidsβ-agonistsOral corticosteroids (40–60 mg/day of oral prednisone) in severe or progressive disease.In refractory cases:Cyclophosphamide & Azathioprine