HYPERSENSITIVITY PNEUMONITIS

WHEN BREATHING AIR EVERYDAY BECOMES A HIDDEN TRIGGER, THE LUNGS MAY QUIETLY SUFFER-THIS IS THE STORY OF HYPERSENSITIVITY PNEUMONITIS.

HYPERSENSITIVITY PNEUMONITIS (HP) is an immune mediated response that takes place in the lungs. It happens when there is continuous inhalation ( breathing in) of certain organic and inorganic dust particles

(1-5microns size) from the environment or work place, leading to strong immune reaction / hypersensitive reaction inside lung. The inflammatory reaction develops inside alveoli (air sacs) and small air passages

( bronchioles). Previously it was called extrinsic allergic alveolitis.

The first description of HP came out in 1932, when it was observed in maple bark workers due to fungal exposure, in Michigan company.Later it was observed in farmers exposed to mouldy hay in England (Farmer's lung).

Over 300 substances have been identified to cause HP varying from bacteria, fungi,animal/bird/plant protein to certain chemical and metal dust.

The immune response of HP is explained by the genetic susceptibility in some individuals like variations in MHC( Major Histocompatibility Complex), implying complex interplay between host and environmantal factors. Cigarette smoking appears to decrease the risk of developing HP. However, a smoker who develops HP will have a more serious course associated with high mortality.

WHAT ARE THE MOST COMMON CAUSES RESPONSIBLE FOR HP?

COMMON ORGANIC AND INORGANIC CAUSES

The most commonly reported occupational/ environmental causes of Hypersensitivity Pneumonitis are:

ORGANIC CAUSES:

FARMER'S LUNG: Agricultural workers inhaling dust of moldy spores from damp hay,straw,grain,silage etc., can be associated with livestock farming.

BIRD /PIGEON FANCIER'S LUNG: It is caused by chronic exposure to organic antigen present in bird's droppings, feathers . Indirect exposure to feather beddings,comforters also may cause the disease.

ALL BIRDS CAN CAUSE HYPERSENSITIVITY PNEUMONITIS

HOT TUB LUNG: Bacterial contamination by MAIC(Mycobacterium Avium Intra Cellulare) of water in hot tubs,whirlpools,spas

OTHERS are:

BAGASSOSIS ( Moldy sugarcane residue),MUSHROOM WORKER'S LUNG/COMPOST LUNG ( fungal spores in mushrooms or the compost), MALT WORKER'S LUNG( moldy barley during malting).

LESS COMMON CAUSES ARE:

HUMIDIFIER /AC (Air Conditioner) LUNG: Mold/Bacteria contaminated water vapour

WIND INSTRUMENT LUNG: Contaminated Saxophone

BAKER'S LUNG: Fungi/Mites in flour

DUVET LUNG: Feathers in bedding, duvets, pillows

RODENT HANDLER'S LUNG: Proteins in urine/serum of rats

INORGANIC ( CHEMICAL AND METAL) CAUSES OF HP ARE:

CHEMICAL CAUSES ARE:

PAINTER'S LUNG: Isocyanates in spray paints,foams,plastics

PESTICIDE LUNG: Pyrethrum sprays/fog to control pests

ACRYLATES used in dental products, METALS like nickel,cobalt,zinc in metal working fluids can also cause hyper sensitivity pneumonitis.

"ONLY IN LESS THAN 40% OF HP CASES, CAUSATIVE AGENT IS RECOGNISED. REST OF CASES, THE CAUSE MAY NOT BE IDENTIFIED

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WHAT IS THE INCIDENCE OF INTERSTIAL LUNG DISEASE (ILD) DUE TO

HYPERSENSITIVITY PNEUMONITIS?

IN USA- 2%

IN EUROPE- 4-15%

IN INDIA- 47% 9 (ILD REGISTRY)

In INDIA, Avian antigen of pigeons,doves,parrots,cockatiel birds, poultry are commonly found to cause HP.

LENTIL HP caused by aspiration of lentil based weaning food in infants, usually force fed,is occasionally reported by pediatricians in India.

"HYPERSENSITIVITY PNEUMONITIS IS BECOMING MORE COMMON."

HOW IS HP CLASSIFIED?

NON FIBROTIC (purely inflammatory) HP &

FIBROTIC (mixed inflammatory and fibrotic) HP or PURELY FIBROTIC HP

HOW DOES A CHEST PHYSICIAN DIAGNOSE HYPERSENSITIVITY PNEUMONITIS?

HISTORY DETAILS IN HP CASES:

An attack of ACUTE HP typically occurs 4 to 6 hrs after short period of intense exposure to the material responsible for HP. Flu like symptoms with fever, chills, muscle aches, headache and cough are present. These symptoms may last for 12 hours and upto a few days. The symptoms may disappear completely if no further exposure.

In CHRONIC HP where there is repeated or continuous exposure to small amounts of antigen/allergen, symptoms like breathing difficulty, tiredness and cough appear which may last for few weeks or months. There can be weight loss with progressive worsening of the disease.

EXPOSURE ASSESSMENT: History details are obtained to identify the offending cause (antigen).

Exposure to the following at work or home or elsewhere, for example: birds, feathers, fishmeal, grain dust, fertilizers, compost, food or plant products like cheese, mushroom, sugarcane, wheat flour, cotton should be enquired.

Occupational position like painting, welding, carpenting, insulating, baking, pottery making should be enquired. Working in locations like mines, quarries, foundries, papermills, cement factories should be enquired too.

ON PHYSICAL EXAMINATION, inspiratory squeaks or crackless might be be heard.

INVESTIGATIONS FOR DIAGNOSIS OF HP:

1.HRCT SCAN OF CHEST :

In HP two patterns are described to suggest the diagnosis of HP.

1. Non fibrotic HP pattern: Air trap, ill defined centrilobular nodules, mosaic attenuation, ground glass opcities. These features are seen predominantly in upper lobes and middle lobes. Such findings suggest 'reversible active inflamation'.

Fibrotic HP pattern: Hexagonal pattern, three density/ head cheese sign, reticulations, traction bronchiectasis, cystic changes are suggestive of irreversable fibrosis or scarring.

NON FIBROTIC PATTERN AND FIBROTIC PATTERN

2. BRONCHOSCOPY ( FOB) : Broncho Alveolar Lavage or BAL fluid analysis:

Cellular analysis showing Lymphocyte count > 30% is highly HP specific.

Flow Cytometry showing low CD4/CD8 is sugestive of HP.

3. ABG (Arterial Blood Gases) will demonstrate Hypoxia and Hypocarbia

( low PaO2 and low PaCO2).

4. SPECIFIC IgG or PRECIPITIN tests for specific antigen helps to confirm suspicious exposure. But no well defined predicted values are available. The presence indicates only sensitization and does not confirm diagnosis.

5.LUNG BIOPSY: It is done following MDD(Multi Disciplinary Discussion), when there is difficulty in diagnosis. Usually it is done by Trans Bronchial Forceps Lung Biopsy(TBLB) or Trans Bronchial Lung Cryobiopsy(TBLC) .Rarely Surgical Lung Biopsy is needed. The HistoPathological Examination demonstrating cellular interstitial pneumonia , cellular bronchiolitis with poorly formed non necrotising grannulomas is highly suggestive of HP.

6. PULMONARY FUNCTION TESTS:

SPIROMETRY will often demonstrate RESTRICTIVE pattern with reduced FEF.

LUNG volumes and DLCO,6MWD are reduced. ABG will demonstrate hypoxaemia and hypocarbia.

HOW IS HYPERSENSITIVITY PNEUMONITIS MANAGED?

MANAGEMENT LINES OF HYPERSENSITIVITY PNEUMONITIS

ELIMINATION OF CAUSATIVE AGENT IS THE PRIMARY LINE OF MANAGEMENT.

Eg. Removal of the source like pets, feather filled bedding, Repair of any water damage to walls,carpets etc, Proper maintenance of humidifiers,AC systems, Air quality improvement by using HEPA filters,Occupational prevention like wearing PPE, engineering controls or a job change.

ACUTE HP :

Corticosteroids given for initial improvement in acute exposures. But it may not prevent progression to fulminant HP.

ACUTE/CHRONIC HP CASES:

IMMUNOMODULATORS: MMF and AZATHIOPRIM may improve the DLCO and FVC after using for one year.

RITUXIMAB/LEFLUNAMIDE for 6 months led to stabilisation in some.

PROGRESSIVE FIBROTIC ILD-HP: ANTIFIBROTIC THERAPY.

OTHERS:

SUPPORTIVE symptomatic treatment

LTOT ( Long Term Oxygen Therapy /Home Oxygen Therapy)

VACCINATIONS

PULMONARY REHABILITATION

LUNG TRANSPLANTATION: Excellent Median Survival is noticed in HP cases who underwent Lung Transplantation compared to Lung Transplantation in UIP-IPF cases.

PERSONAL PROTECTIVE EQUIPMENT AND HEPA FILTERS TO PROTECT FROM ORGANIC AND INORGANIC PARTICLES AS SMALL AS 3 MICRONS

POOR PROGNOSIS SEEN IN:

PROGRESSIVE FIBROSIS ,median survival is 3-5 years.

Older age, Male sex.

Longer and greater exposure to causative antigen

Delayed diagnosis

Cigarette smokers

Absence of BAL lymphocytosis

Recurrent acute exacerbations

PAH

Low DLCO,FVC

Extent of fibrosis on HRCT scan.

"HYPERSENSITIVITY PNEUMONITIS IS A WELL MANAGEABLE DISEASE WHEN DIAGNOSED EARLY. IDENTIFYING THE TRIGGER CAUSE AND STARTING TREATMENT EARLY CAN REDUCE THE INFLAMMATION AND PROTECT LUNG FUNCTION.IF YOU ARE IN AND AROUND VIZAG AND EXPERIENCE PERSISTANT COUGH, BREATHLESSNESS OR UNEXPLAINED FATIGUE, CONSULT DR. CHUKKA BHARAT, AN EXPERIENCED PULMONOLOGIST."