Hyprsensitivity depending on the amount of inhaled antigen and

Hyprsensitivity pneumonitis (HP) previously called extrinsic
allergic alveolitis  is a non Ig E immune
mediated  disorder in the lungs  arising from the sensitization and repetitive
exposure to any of a wide variety of organic dust in a susceptible host 1.Incidence
of HP is highly variable worldwide  and
related to exposure risk. The antigens that cause HP have been categorized in
to microbial (fungal or bacterial), animal or chemical sources. Antigens
associated with HP are smaller than 3 µm, giving them ability to deposit in
terminal small airways and alveolar spaces. Hypersensitiviy pnemonitis accounts for 5
-15% of ILD burden 2

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

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Bird Fanciers lung disease(BFL) is the most common
type of HP  and caused by air borne
exposure to avian antigens4,5.BFL also known as pigeon fanciers lung and is
mainly seen among pigeon and budgerigar fanciers6.

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

 

Acute form usually presents
following high level of exposure and the symptoms develop within 6-8 hours.
Acute form characterized by high fever with chills, myalgia, fatigue, headache,
dry cough and symptoms usually disappear in 24 hours. Sub acute form is usually
due to relatively low levels of exposure and takes longer to develop symptoms. Chronic
HP occurs with long term, low level exposure to the antigens which lead to
irreversible pulmonary damage without acute attacks 8.

 

Most
of the time acute and sub acute form of disease 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 and treat early.

There
is no specific immunological, radiological or physiological diagnostic test for
HP and diagnosis is mainly dependent on clinical judgment.

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
possible 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 categorizing 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.

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