Name
HYPERSENSITIVITY PNEUMONITIS
DESCRIPTION
DETAIL
CAUSES . Exposure to dust capable of inciting immune response, for example: . Farmers lung (Thermophilic actinomycetes) . Air conditioner lung (Thermophilic actinomycetes) . Bagassosis (Thermophilic actinomycetes) . Bird breeders lung (avian protein and blood) . Rat handlers lung (rat urine and protein) . Isocyanate lung (toluene diisocyanate [TDI], methylene diisocyanate [MDI] exposure) . Washing powder lung (Bacillus subtilis enzymes) -------------------------------------------------------------------------- DIFFERENTIAL DIAGNOSIS . Acute hypersensitivity pneumonia: . Acute infectious pneumonia . Influenza . Adenovirus . Mycoplasma . Pyogenic bacteria . Pneumocystis carinii . Fungus . Chronic hypersensitivity pneumonia: . Tuberculosis . Sarcoidosis . Pneumoconiosis . Scleroderma . Rheumatoid lung . Lupus erythematosus . Eosinophilic granuloma . Lymphangitic carcinomatosis . Fungal infections . Pneumocystis carinii pneumonia . Drug reactions . Hemosiderosis . Idiopathic pulmonary fi brosis* LABORATORY β’ Leukocytosis with polymorphonuclear predominance in acute form β’ Non-specific elevation of immunoglobulins and erythrocyte sedimentation rate β’ Positive rheumatoid test and mononucleosis spot test β’ Negative blood, sputum, throat cultures * SPECIAL TESTS * Serum IgG precipitating antibodies to offending agent. Note: 40-50% of non-hypersensitive individuals with high exposure have positive precipitating antibodies. * Skin testing: Standardized agents poorly available and of limited use * Inhalation challenge testing can cause severe reactions and therefore is usually not performed except in specialized, in-hospital units * Pulmonary function studies demonstrate: . Reduced lung volume, Impaired gas transfer, Forced expiratory volume (FEV) 1, forced vital capacity (FVC) and FEV1/FVC ratio may be normal early on and then drop with the development of chronic airway obstruction, Forced expiratory flow (FEF) 25-75 and flows near residual volume may be reduced, Decreased lung compliance * Bronchoalveolar lavage : . Acute form with neutrophils and lymphocytes . Chronic form with high lymphocytes (60%) mostly T-cells of CD-8 type . Differentiate from sarcoid which has mostly T-cells of CD-4 type * Lung biopsy - Rarely needed if treatment and avoidance of exposure results in improvement * IMAGING . Acute hypersensitivity pneumonitis on CXR: 30-40% abnormal CXR - Diffuse interstitial infiltrate with hazy background, Fine nodular shadows from 1-3 mm in size, Linear striated shadows, Occasional lower lobe consolidation, Resolution between attacks . Chronic hypersensitivity pneumonitis on CXR: Reticulonodular pattern, Linear shadows and nodules change from fine to coarse pattern with progression of disease, No hilar adenopathy, pleural effusion, or pneumothorax, Upper lobe predominance in 40-50% of cases with ring shadows and bronchiectasis * DIAGNOSTIC PROCEDURES . Lung biopsy rarely needed for diagnosis . Role of CT scan is unclear
TYPENOTES
RISK FACTORS: Intensity of exposure, Size (1-5 micron particles reach deep into lung), Smokers at lower risk than non-smokersGENERAL MEASURES Avoidance of offending antigen DRUG(S) OF CHOICE β’ Avoidance is primary therapy β’ Corticosteroids: Prednisone, 2 mg/kg/day or 60 mg/m2/day, or other comparable corticosteroid. Initial course of one to two weeks with progressive withdrawal of medication. Alternate day therapy if exposure cannot be discontinued may help, but may not prevent progression. ALTERNATIVE DRUGS β’ Bronchodilators may symptomatically improve patients β’ Oxygen may be needed in advanced cases PATIENT MONITORING Initial followup should be weekly to monthly depending upon severity and course PREVENTION/AVOIDANCE Antigens must be avoided to stop process POSSIBLE COMPLICATIONS β’ Progressive interstitial fi brosis with end-stage lung disease β’ Corpulmonale and right heart failure EXPECTED COURSE/PROGNOSIS β’ Excellent prognosis with reversal of pathologic findings with effective treatment of early disease β’ Stabilization of severe, advanced disease with avoidance and anti-inflammatory medication
RELATED DISEASE
Not Available Disease
DISEASE
INVESTIGATION
X-RAY CHEST P.A. VIEW( NORMAL ), COMPLETE BLOOD COUNT, PULMONARY FUNCTION TEST, BRONCHO-ALVEOLAR LAVAGE FOR CYTOLOGY