HYPERSENSITIVITY PNEUMONITIS Clinical features Diagnosis and Treatment of Hypersensitivity

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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.

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.

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.

•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.

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.

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.

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.