4. Background
• 1st described in early 1900s
Farmer’s lung: fermers who reported febrile
episodes after exposure to mouldy grains,hay or
straw
Reed and barbee in 1965
pigeon breeder’s lung:relationship between hp
and exposure to avian antigens
Hendrik and colleagues in 1978
Budgerigar fancier’s lung
5. DEFINITION
• Hypersensitivity pneumonitis (HP), also called
extrinsic allergic alveolitis, is a respiratory
syndrome involving the lung parenchyma and
specifically the alveoli, terminal bronchioli, and
alveolar interstitium, due to a delayed allergic
reaction.
• Such reaction is secondary to a repeated and
prolonged inhalation of different types of organic
dusts or other substances to which the patient is
sensitized and hyper responsive,
6. PREVALENCE
• In the US HP accounted for less than 2% of the
patients with interstitial lung disease (ILD),
whose yearly incidence was calculated to be
about 30 per 100,000 .
• In Europe, according to ILD registries, HP
affects from 4 to 15% of all ILD cases .
7. CAUSATIVE AGENT
• Hypersensitivity pneumonitis can be caused
by multiple agents that are present in work
places and in the home, such as microbes,
animal and plant proteins, organic and
inorganic chemicals.
13. CLINICAL FEATURES
13
• Depends upon nature of the inhaled dust,
such as antigenicity, particle size, intensity and
frequency of exposure to the antigens, the
immunological response of the host and
concomitant bacterial or viral infections.
• Clinically HP can be categorised into acute,
subacute, and chronic forms.
14. The acute form
• Presents after a high-level of exposure to the
offending antigen over a short period of time.
• Symptoms usually develop within 4 to 8 hours
and are similar to acute viral infection.
• Symptoms may include high fever up to 40 oC,
chills, myalgia, fatigue, dyspnoea, and non-
productive cough.
• Bibasilar end inspiratory rales are prominent
and may persist for weeks after the fever
subsides.
15. Subacute Form
• The symptoms are more insidious in the subacute
form of HP due to the repeated low-level exposure.
• progressive respiratory symptoms over weeks-to-
months without acute systemic symptoms as noted
with the acute form.
• Physical examination often reveals crepitant rales
and hypoxemia especially with exertion.
16. Chronic HP
• Results from prolonged and continuous exposure
to low-levels of antigens leading to irreversible
pulmonary damage without major acute attacks.
• Progressive dyspnoea, cough, malaise, weakness,
anorexia, and weight loss are common. Fever is
often not present.
• Interstitial fibrosis is prominent.
• Lung examination may demonstrate dry crackles,
but wheezing is uncommon.
End-stage disease: cyanosis & right-sided
HF
17. Laboratory Diagnosis
↑ Specific IgG against the offending antigen
↑ ESR & CRP
↑ IgM , IgA, IgG
↑ ANA
IgE:Normal
Eosinophil count:Normal
BAL fluid study: ↑Lymphocyte count
↑ IgG
17
18. PFT
There is no single characteristic pattern of
pulmonary function abnormalities .
Acute HP : restrictive pattern
Subacute and chronic HP : air way obstruction or
mixed
↓ DLCO (most sensitive physiologic test in early HP )
18
20. Ground glass pattern
Most common in acute HP (but may also be seen in
subacute and chronic HP)
Middle lung zone
PFT: restrictive , ↓DLCO
May resolve with removal from exposure
20
24. Centrilobular nodules
Round, poorly defined, less than 5 mm in diameter
Typically centrilobular
Profuse throughout the lung,but a middle to lower
lung zone predominance.
Most frequent HRCT finding in HP
Centrilobular nodules + ground glass
opacification are highly suggestive for HP.
PFT : May be normal
24
25. Fibrosis
Chronic HP (subacute HP)
Irregular linear opacities
Traction bronchiectasis
Honeycombing
25
26. Emphysema
Chronic HP
Emphysema occurred more commonly than
fibrosis in chronic farmer’s lung.
26
38. Clinical Prediction
• 1. Exposure to known offending antigen
• 2. Positive precipitating antibody to the
offending antigen
• 3. Recurrent episodes of symptoms
• 4. Respiratory crackles in physical examination
• 5. Symptoms occurring between 4 to 8 hours
after exposure
• 6. Weight loss
39. • Major Criteria (Four major criteria need
to be present)
• 1. H/O symptoms compatible with HP
• 2. Evidence of exposure to the offending antigen
by history or through detection in serum or BAL
fluid antibody
• 3. Changes of characteristic HP on chest
radiograph or HRCT of chest
• 4.BAL fluid lymphocytosis,
• 5. Demonstration of histologic changes consistent
with HP
• 6. Positive ‘natural challenge’ that produces
symptoms
Diagnostic criteria for hp:
Adapted from Schuyler and Cormier (1997)
40. Minor Criteria (Two minor criteria
need to be present)
• 1. Bibasilar rales
• 2. Decreased diffusion capacity
• 3. Arterial hypoxemia, either at rest or with
exercise
41. TREATMENT
Cornerstone of therapy → removal from exposure
Respirators are used when removal from exposure is
impossible.
Oxygen (hypoxemic patients)
Opoids:Control of cough
Airflow limitation:
Inhaled steroids
β-agonists
Oral corticosteroids (40–60 mg/day of oral prednisone)
in severe or progressive disease.
In refractory cases:
Cyclophosphamide & Azathioprine
No evidence on the efficacy of anti-fibrotic agents in
the treatment of chronic HP. 41
42. PROGNOSIS
The clinical course of HP is variable
Acute HP generally resolves without sequelae
But progressive impairment may occur with recurrent
attacks or with a single severe attack.
Subacute or chronic forms of HP present with
insidious symptoms
More subtle clinical abnormalities
Frequently recognized later in the disease course
Long-term mortality rates for patients with chronic
HP range from 1% to 10%.
42
43. Poor Prognostic factors
Older Age
Exposure for a longer period
Greater intensity of exposure
Digital clubbing
Histologic pattern of NSIP or UIP
43
44. Take home message
• HP results from an exacerbated immunologic
response to inhaled antigens.
• Menifestation ranging from infection-like acute
symtoms to subacute &chronic interstitial disease
• When exposure to antigen persists,permanent lung
damage may occur
• 1st line Rx for HP is withdrawl of contact with the
offending Ag.
• Oral corticosteroids,depending on the severity of
presentation.