HYPERSENSITIVITY PNEUMONITIS Clinical features Diagnosis and Treatment of Hypersensitivity


  • It is also called extrinsic allergic alveolitisis an inflammatory disease of alveolar walls, and terminal airways caused by repeated exposure to organic agents in a susceptible person.
  • It’s also called farmer’s lung, commonly due to the HP caused by moldy hay.
  • Usually the organisms responsible for the hypersen­sitivity reactions are Actinomyces, Micropolyspora faeni and Aspergillus.

HYPERSENSITIVITY PNEUMONITIS Clinical features Diagnosis and Treatment of Hypersensitivity


  • Acute form: Develops 2–9 hours following exposure
  • Cough, dyspnea, fever, chills, diaphoresis, headache, nausea
  • Symptoms last hours to days

Chronic form: Develops after several months of exposure:

  • Progressively worsening cough and dyspnea
  • Also develop fatigue, weight loss, anorexia

Subacute form: Develops after several days to weeks:

  • Marked by worsening respiratory symptoms

Other important points in history include:

  • History of pulmonary disease or recurrent infections
  • Recent change in work or home
  • Known exposure to pets, hot tubs, areas with water damage
  • Symptomatic improvement when away from work or home

HYPERSENSITIVITY PNEUMONITIS Clinical features Diagnosis and Treatment of Hypersensitivity 2

Etiology of Hypersensitivity

  • · Different names are given to the different dis­eases depending on the occupation of host, the antigen’ exposed to, and the habit of the person.
  • E.g. Farme(s lung due to moldy hay.
  • · Chemical wo kers lung
  • · Mushroom worker’s disease
  • Bagassosis in sugarcane workers
  • Wood workers’ lung.
  • Humidity, temperature, concentration of antigen, du­ration of exposure and habits like smoking all increase the incidence of HP.

Clinical features of Hypersensitivity

  • There is Lnterstitial pneumonitis.
  • · Presentation may be acute, subacute or chronic.
  • · Symptoms are cough, fever, dyspnoea, chills, malaise, from 6-8 hrs after exposure, to months from onset. Symptoms may persist for years.
  • · In chronic form, there is pulmonary fibrosis, cy­anosis, clubbing, pulmonary hypertension, res­piratory failure and death.
  • · On physical examination, there are bilateral basal crackles, reduced carbon monoxide diffusion capacity, and hypoxemia.

Diagnosis of Hypersensitivity 

Lab Tests —

  • •May have increased inflammatory markers (erythrocyte sedimentation rate, C-reactive protein)
  • •Leukocytosis and increased gammaglobulins typically seen
  • •Specific IgG antibody to offending agent can be detected and checked serially to detect response to treatment :
  • Not always present (likely because many unknown antigens)
  • Low specificity (10% of people exposed to farmer’s lung antigen develop antibodies; only 0.3% show symptoms)
  • •Rheumatoid factor often positive (unknown cause)
  • •Negative blood, sputum, throat cultures
  • •Bronchoalveolar lavage (BAL)
    • Acute form with neutrophils and CD4 T lymphocytes
    • Chronic form with high number of CD8 T lymphocytes
    • BAL may help to differentiate chronic hypersensitvity pneumonitis from sarcoid, which has high CD8 T lymphocytes
  • -There is neutrophilia, lymphopenia, increased ESR, increased C reactive protein, rheumatoid factor, raised serum immunoglobulins.

Chest x-ray

    • Acute: Diffuse ground-glass infiltrates, nodular or striated patchy opacities. Up to 20% have normal CXR.
    • Subacute: Same as acute, may have sparing of lung bases
    • Chronic: Upper lobe fibrosis, reticular opacities, volume loss, honeycombing
    • may be normal or show patchy or dif­fuse infiltrates or discrete nodular infiltrates. There may be honey-combing.

CT scanning

    • is diagnostic showing the details of fi­brosis, and nodules.

Pulmonary function test (PFT)

    • shows a restrictive or obstructive pattern, decreased lung volume, im­paired diffusion capacity, bronchial hyper reactivity and reversibility.
  • BAL (Broncho alveolar lavage)
    • shows lymphocytic alveolitis.
  • Lung biopsy through bronchoscopy, may be diagnostic.
  • Inhalation challenge i.e. a positive response to in­haled antigen may be done for transient airflow ob­struction.

Treatment of Hypersensitivity

  • The condition should be diagnosed by occupa­tional history, lifestyle, livelihood, Hlo exposure to antigens .
  • The exposure should be checked by wearing of appropriate masks, pollen masks, personal dust respirators, air helmets, ventilated helmets with fresh air.
  •   Glucocorticoids – Prednisone 1 mglkglday for 1-2 weeks tapered in 6 wks. Maintenance dose may be continued at the lowest possible dosage if symptoms recur.
  • •Avoidance of offending antigen is primary therapy.


    • Prednisone: 1–2 mg/kg/day, to max of 50–60 mg p.o. daily
    • Initial course of 1–2 weeks with progressive taper
    • Low-dose therapy (20 mg p.o. daily) may be as effective as avoidance.
Contraindications  : Refer to the manufacturer’s literature.
  • •Precautions: Observation for side effects:
    • Acne
    • Hirsutism
    • Behavioral changes
    • Immunosuppression
    • Salt and water retention
    • OsteoporosisWeight gain/appetite increase


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