| What is hypersensitivity pneumonitis? | AKA extrinsic allergic alveolitis, immuno-induced non-IgE mediated inflammatory lung disease resulting from sensitization and subsequent recurrent exposure to inhaled dust |
| How is the epidemiology of hypersensitivity pneumonitis? | Varies widely, 8.5% (half of them only have clinical manifestation) in agricultural areas
Pigeon breeders 40-50% (and disease manifestation occurs in 6-21%)
Outbreak from microbial contamination is 15% attacks and 70% exposed.
Host factors are important (less frequent in non-smokers, atopic pt are not at increased risk, viral infections may play a role |
| How is the pathology of HP? | Diffuse mononuclear and lymphocytic inflammation of terminal bronchioles, interstitium and alveoli
Little involvement of larger airways
Lymphocytes and monocytes may accumulate and organize as granuloma and may cause fibrosis.
Also maybe multinucleated giant cell/ central fibrosis |
| What are the inciting agents causing HP? | Disease caused by inhaling organic dust/ inorganic chemicals in a sensitized individual.
Major factor is the size (>10mcm stopped in nose, 5-10mcm cleared by cilia/ extrinsic asthma, 0.3-5 mcm reach alveoli cleared by macrophages or cause HP)
It was though to be an occupational hazard/ recreational/ environmental.
Associated diseases: Bagassosis (moldy sugar cane), Farmer's lung (inhaled actinomycetes [micropolyspora faeni - in hay/soil/ grain/ AC/ humidifiers/ pools/ furnaces])
Inhalation of animal products [serum protein, urine protein, feathers - bird fancier's lung/ gebril keeper lung/ turkey handler lung]
hapten protein chemicals
Drugs [HP-like illness- amiodarone, gold, minocyclin, cocaine] |
| How is the clinical presentation of HP? | Similar regardless of inciting agent, acute/subacute/chronic (multiple episodes of acute or prolonged subacute) |
| How is acute HP? | Caused by brief intense exposure, 4-8 hours after exposure we have flu-like illness (cough, dyspnea, tachypnea, rales, chills, fever, malaise, diaphoresis, headache and myalgias)
Symptoms last 12-24 hours, peak at 8-12 hours
Between attackes pt is asymptomatic
In acute febrile episode occurs after each contact with antigen |
| How is subacute HP? | Less intense more prolonged exposure, insidious onset, resemble chronic bronchitis (cough, exertional dyspnea, malaise, anorexia, fatigue, weightloss)
symptoms less specific and not associated with exposure, dx is challenging |
| How is chronic HP? | Unrecognized subacute HP can progress to become chronic, S&S are those of chronic pulmonary fibrosis (lung damage)
Indistinguishable from end-stage IPF. |
| How is the pathogenesis of HP? | Occurs with exposure to correct size and composition dusts (0.5-5 mcm, antigenic, resistant to degradation and persists long enough in lung tissues for sensitization)
Pt must be senstized during a pervious exposure, sensitization durationis variable (months to years), not all subjects get sensitized.
Proinflammatory cytokines (IFN-gamma, IL10, TNF) activated macrophages, CD8 lymphocytes and form granuloma promoting fibrosis
Type III and IV (and some I and II) hypersensitivty caused lung injury followed by T cell mediated hypersensitivity, inflammation, granuloma formation, fibrosis. |
| How is the dx of HP? | Combination of symptoms, PE, radio, PFT and immuno serology
High sus in pt with recurrent bouts influenza like illness/ ILD leading to a complete history |
| What is the imaging findings in HP? | CXR normal or subtle reticulonodular change, patchy interstitial infiltrates, abnormalities return normal days to weeks after acute episode
HRCT: centrilobular micronodules and ground-glass opacities (specific for HP)
may be indistinguishable from IPF with reticular pattern and honeycombing |
| What is the result of PFT in HP? | Restrictive impairment + diffusing capacity impairment
Return normal after weeks of acute episode, progressive and irreversible restrictive changes occur in chronic form |
| What are tests done for dx of HP? | Skin testing not used
Serum precipitins (with IgG/ IgM and IgA)
Precipitating Ab (90%) but not for screening.
BAL: increased lymphocytes with low CD4/CD8 ratio |
| What is the result of biopsy in HP? | Biopsy taken for dx, distinctive histopathology according to disease stage
surgical biopsy ez diagnosis than transbronchial
Acute HP alveolar and interstitial accumulation of leukocytes, fluids and macrophages centrilobular.
Subacute/chronic: predominant lymphocytes plasma cell, macrophage infiltration (alveolar) - 70% loose non-caseating granulomas, 65% shows degres of fibrosis, 60% bronchiolitis obliterans) |
| What are the criteria of dx of HP? | Exposure to a known Ag, positive precipitating Ab to Ag, recurrent episodes of symptoms, inspiratory crackles examination, symptoms occurring 4-8 hours, weight loss (6 criteria) |
| What is the therapy of HP? | Aviodance, change in industrial procedures, antipyretics and O2 may be needed, bronchodilators not benificial
Corticosteroids (prednisone 0.5-1) for 1-4 weeks may decrease toxicity of acute HP but no long term advantage
Longer treatment needed for subacute, once chronic any tx is of marginal benifit |
| How is the prognosis of HP? | Acute: complete recovery, symptoms disappear 12-48 h, fatigue, lassitude, and exertional dyspnea may last for weeks, pt asymptomatic between attacks
Subacute: aviodance--> symptoms disappear, continued exposure 30-60% of pt of farmer's lung were disabled in 5 years, 10-15% were dead
Pigeon breeders 5-year mortality 30%, some disease progressed despite avoidance.
Chronic form: deterioration to respiratory insufficiency likely, but end-stage disease is not uniform finding |
