Hypersensitivity pneumonitis is a lung disease caused by an allergic reaction to inhaled organic dusts or chemicals. It can present acutely with fever and respiratory symptoms or chronically with fibrosis. The diagnosis is based on exposure history, symptoms improving away from exposure, and radiologic/pathologic findings. Treatment involves identifying and removing the causative agent along with corticosteroids in more severe cases. Prognosis depends on the severity and duration of exposure, with chronic forms at higher risk of permanent lung damage.

1. GOOD
MORNING

2. WELCOME TO WEEKLY
MORNING PRESENTATION

3. Hypersensitivity pneumonitis: a complex lung
disease
PRESENTED BY
DR.MD.SHARIF AHSAN
RESIDENT(PULMONOLOGY)
PHASE-A

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.

8. CAUSATIVE AGENT....
Three main categories:
 Microbial agents
 Bacteria
 Farmer’s lung
 Bagassosis
 Mushroom
worker’s lung
 Fungi
 Wood pulp
worker’s lung
 Cheese washer
lung
 Ameba
 Humidifier lung
Animal proteins
Avian proteins
 Bird breeder’s lung
Urine,Serum,Pelts
 Animal handler’s
lung
Wheat weevil
Wheat weevil lung
 Chemicals
 Isocyanate
 TDI,MDI,HDI
 TMA
 Trimellitic
anhydride
8

9. 9

10. PATHOGENESIS
Host factors:
 Host susceptibility (Genetic factors)or
resistance factors may influence individual
responses to inhaled antigens.
 Non smokers > smokers
Exposure factors:
 Ag concentration
 Duration of exposure
 Frequency & intermittency of exposure
 Particle size
 Use of respiratory protection
 Farmer's lung disease: winter
 Bird breeder's lung: summer 10

11. PATHOGENESIS....
Immunology:
 Repeated inhalation of antigens → sensitization →
immunology response(type III,IV) → influx of
neutrophiles → shift T lymphocytes
(~70%)(predominantly of CD8)(↓CD4/CD8 )
 ..DesktopHypersensitivity
Pneumonitis_HD.mp4 11

12. PATHOGENESIS....
12

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

19. CXR
Acute HP:
 Diffuse ground glass opacification
 Fine nodular or reticulonodular pattern( lower
lung field)
 Consolidation ( rarely )
Subacute HP:
 Reticulonodular pattern
Chronic HP:
 Fibrosis with upper lobe retraction
 Reticular opacity
 Volume loss
 Honeycombing
 Mediastinal lymphadenopathy (up to 50%) 19

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

21. Acute HP: pigeon breeder’s lung shows ground-glass
haziness and associated air-trapping
21

22. Airspace consolidation
 Only reported in
acute HP
 Bilateral ill-defined
areas of
consolidation
22

23. Subacute HP: bilateral alveolar and
reticular pattern
23

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

27. Chronic HP: upper lobe fibrosis
27

28. Chronic HP: farmer’s lung disease showing bibasilar
end-stage fibrosis
28

29. HRCT
 Sensitivity of HRCT is significantly better than CXR
 Ground glass
 Centrilobular nodules
 Fibrosis
 Emphysema
 Mediastinal lymphadenopathy (> 20 mm )
29

30. Centrilobular ground-glass nodules uniformly
distributed throughout the lung.
Lobular air-trapping also frequently present.
30

31. Multiple low density ill-defined centrilobularnodules
31

32. Extensive areas of grand-glass attenuation.
Decreased perfusion (arrows)representing
associated air-trapping.
32

33. Chronic HP: Honeycombing, intralobular and septal
fibrosis, architectural distorsion
33

34. Mosaic pattern
 Patchwork of regions of differing attenuation
 Due to patchy areas of ground glass or
airtrapping
34

35. Lung Biopsy
 Classic triad:
 Cellular bronchiolitis
 Lympho-plasmocytic interstitial infiltration
 Non-necrotizing granulomas
35

37. Diagnosis
 Temporal relationship between symptoms
and certain activities is often the first clue
to the diagnosis of HP
37

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.