Hyprsensitivity pneumonitis (HP) also known as extrinsic
allergic alveolitis is a non Ig E mediated immune lung disease arising from the
sensitization and repeated exposure to any of a wide variety of organic dust
1.Incidence of HP is highly variable worldwide  and related to exposure risk. The antigens
that cause HP can be arising from microbial (fungal or bacterial), animal or
chemical sources. Antigens associated with HP are smaller than 3 µm , allowing
them to be deposited in distal small airways and alveolar spaces. Hypersensitiviy
pnemonitis is known to contribute to 5 -15% of ILD burden 2

 

Non necrotizing granuloma, chronic inflammatory
change in smaller airways and diffuse interstitial infiltrates of chronic
inflammatory cells are the main three histological characteristics of HP 3

Bird Fancier,s lung disease(BFL) is a type of lung
disease caused by air borne exposure to avian antigens4,5.BFL is probably
one of the most common types of HP and is mainly seen among pigeon and
budgerigar fanciers6.

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Classically, the clinical
presentation has been divided into acute , sub acute and chronic forms
depending on the amount of inhaled antigen and repeated exposure.7

 

Acute form usually presents after
high level of exposure and the symptoms develop within 4 to 8 hours of exposure.Acute
form characterized by high fever with chills, muscle aches, fatigue, body malaise
and a dry cough. Sub acute form is due to relatively low levels of exposure and
the symptoms appear more insidiously. Chronic HP occurs with prolonged low
level exposure to the antigens which lead to irreversible pulmonary damage
without acute attacks 8.

 

Acute
and sub acute form of disease most of the time resolve by the avoidance of
exposure. Chronic HP is a potentially serious disease which may be progressive,
irreversible, and result in debilitating fibrotic lung disease 9.It may lead
to respiratory failure.

Prompt diagnosis of HP is important, as the disease
is reversible when diagnosed early in its course.

Diagnosis
of HP is heavily dependent on clinical judgment and there is no specific immunological,
radiological or physiological diagnostic test for HP.

Diagnosis is based upon exposure history, clinical evaluation,
radiographic and physiologic finding and in certain instances, the result of avoidance
the suspected etiologic exposure would help. Other tests, such as
bronchoalveolar lavage (BAL) and lung biopsy, are helpful in excluding other
potential diagnoses and in lending further support to the diagnosis of HP.
The
characteristic BAL found in hypersensitivity pneumonitis (HP) is a
lymphocytosis, though we did not have facility to perform BAL full report on
our patient.  

HRCT is useful in diagnosing and separating the
clinical forms of HP. HRCT may be normal in patients with symptomatic acute HP 10.
When abnormal, more frequent findings are ground-glass opacities or poorly
defined small nodules 1112.Diffuse areas of dense air-space consolidation
may be associated with ground-glass opacities12.

Because of the significant overlap in clinical cases
of sub acute and chronic HP, the HRCT patterns are more variable.
Ground-glass opacities or poorly defined small nodules are common in sub acute
HP. In fact, HRCT of our patient does not reveal
typical features of sub acute hypersensitivity pneumonitis which are ground-glass opacities, air trapping, and
centrilobular ground-glass opacities.

Classical
 HRCT evidence in chronic HP are the
combination of reticular, ground-glass, and centrilobular nodular opacities
associated with features of “fibrosis”  including
interlobular septal thickening, traction bronchiectasis, volume loss, , and
honeycombing) 11.

 Treatment
strategies include environmental control and medical therapy. Antigen avoidance
and removal is the single most important fact in the treatment of BFL and is
crucial in its management 15. Persistent exposure leads to persistent
symptoms and progressive lung damage. Acute & sub acute form of disease may
improve by the avoidance of exposure. Corticosteroids are indicated
for the treatment of severe acute and sub-acute HP and for chronic HP that is
severe or progressive.

 

As our patient had
small joint stiffness along with positive Rheumatoid factor, Rheumatoid
arthritis associated pneumonitis also should be considered as a differential
diagnosis. Rheumatoid arthritis is a systemic
inflammatory disorder mainly affecting the joints, and is associated with autoantibody
production.  Pulmonary involvement is a common extra articular
manifestation, while Interstitial lung disease (ILD) being the primary
pulmonary manifestation of RA13. The two main histopathological patterns of
ILD that are observed in those patients are  the nonspecific
interstitial pneumonia (NSIP) pattern and the usual interstitial pneumonia
(UIP) pattern , while organizing pneumonia,diffuse alveolar damage, lymphocytic
interstitial pneumonia and desquamative interstitial pneumonia are less common
patterns14.

Most of the time Rheumatoid arthritis is diagnosed before
the detection of ILD, but in some cases, respiratory
symptoms may precede articular symptoms.So it is essential to assess signs and
symptoms of connective tissue disease when evaluating a patient with pulmonary
disease of unknown etiology.

Physical examination of patient with Rheumatoid arthritis
ILD   may reveal inspiratory crackles, and restrictive physiology in
spirometry making it indistinguishable from hypersensitivity pneumonitis.

Findings of HRCT favors Rheumatoid arthritis associated organizing
pneumonia which is supported by short history of symptoms in our patient. Histology
of organizing pneumonia would reveal characteristic buds of connective tissue
(Masson’s bodies) in respiratory bronchioles and in alveolar ducts.

The exact mechanism of lung involvement in ILD is yet
unclear and patients with rheumatoid arthritis typically found to have
circulating autoantibodies, the most common being rheumatoid factor and
anti-cyclic citrullinated peptide (CCP) which are thought to have been linked
to the development of ILD.Our patient had positive rheumatoid factor in the serum,
but her anti-cyclic citrullinated peptide (CCP) were negative.

To date, there have been no placebo-controlled
therapeutic trials done in RA associated ILD. No consensus therapeutic guidelines
have been established so far and corticosteroids are the mainstay of therapy
with or without a cytotoxic agent such as azathioprine, cyclophosphamide or mycophenolate
mofetil .Particularly cases of NSIP and Organizing pneumonia( OP) are steroid
sensitive which can be managed with aggressive corticosteroid therapy 16. Moreover,
OP pattern shows rapid treatment response to steroids with a good recovery.

 Possibility of organizing pneumonia due to
bacterial infection which improved with target antibiotic therapy should also
be considered in our patient, who revealed positive BAL culture. But RA -OP is
the primary consideration as her clinical improvement and lung physiology improvement
was achieved only with steroids. 

 

 

CONCLUSION

Hyprsensitivity pneumonitis is
a rare, but a very important diagnosis to be made early to prevent devastating
complications by avoiding exposure to the environmental substances and
early treatment with medicines such as corticosteroids that reduce
inflammation. . If the condition goes undiagnosed and
untreated the chronic inflammation can cause irreversible lung scarring which
leads to poor prognosis.

Hence clinicians should be aware of
its etiology, clinical presentations and should be considered as a deferential diagnosis.
Obtaining proper history is very important to identify the
inciting agent, mainly because the first and most effective treatment is
antigen avoidance and it gives a clue to the diagnosis as well.

As discussed previously, in some rheumatoid arthritis
cases, respiratory symptoms may precede articular
symptoms. Certain sub types of ILD carry excellent treatment response to
therapy and good prognosis. So it is essential to assess signs and symptoms of
connective tissue disease when evaluating a patient with pulmonary disease of
unknown etiology in relevant clinical settings.

 

In our case, it is
a challenge to distinguish HP from connective tissue-related interstitial lung
disease because there was significant exposure to pigeon excreta prior symptoms
appears without characteristic HRCT features of HP along with positive
rheumatoid factor. But with the strong exposure history, sub acute HP would
still be the most probable diagnosis in our patient which nicely responded to
steroid therapy.  

 

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