Fibrosing

NORMAL LUNGS: YOUR LUNGS AS A "TREE"

Your lungs can be likened to a "tree". When you breathe in, air is drawn through the nose and mouth into the windpipe (or trachea). This is the trunk of the tree. From the windpipe, air passes into two large bronchial tubes, one bringing air to each lung. These bronchial tubes are the first "branches" of the tree. They divide into smaller and smaller branches, bringing air into tiny air sacs, called alveoli. The alveoli are the "leaves" of the tree. From these alveoli, oxygen is taken from the breathed-in air and passed into the bloodstream. The oxygen is then taken to all the organs of the body, such as the heart and brain.

EXTRINSIC ALLERGIC ALVEOLITIS: A DISEASE OF THE "LEAVES" OF THE TREE

Extrinsic allergic alveolitis (EAA) is also called hypersensitivity pneumonitis (HP). It is a group of lung diseases affecting the alveoli, or "leaves" of the lung. These diseases are caused by inhaling organic dusts into the lungs through the nose and mouth. Farmer's Lung is the most common type seen in Ireland. It results from inhaling particles (spores) called thermophilic actinomycetes from mouldy hay. The second most common type in Ireland is "Pigeon breeder's Lung" or "Bird Fancier's Lung". This is caused by inhaling proteins from bird droppings. Other much less common examples are humidifier lung (inhaling bacteria from humidified water), byssinosis (inhaling cotton fibres) and bagassosis (inhaling sugar cane fibres). These particles are so small (only 1-5 micrometres in diameter), they can flow down the branches of the lung tree easily, and become lodged in the leaves (alveoli). There are cells in the lung that are part of the lung's immune system. These cells normally protect the lung against injury by viruses, bacteria, inhaled chemicals and other potentially harmful things. In extrinsic allergic alveolitis, when the organic dusts are inhaled, these immune cells start producing harmful chemicals. These chemicals damage the alveoli, causing inflammation. If there is constant (or chronic) inhalation of the dusts, the alveoli may become scarred. This is important as inflammation is generally reversible, either by itself or with treatment, whereas scarring is usually irreversible. In either case, these inflamed, or scarred, alveoli do not take up oxygen as well from the breathed-in air. This leads to low levels of oxygen in the blood. Farmer's Lung and Bird Fancier's Lung are by far the most common forms of extrinsic allergic alveolitis seen in Ireland, and are representative of the condition.

WHAT SORT OF PEOPLE GET EXTRINSIC ALLERGIC ALVEOLITIS?

Farmer's Lung is seen in people who are frequently exposed to hay that has become mouldy. For reasons that are not known, only a small number of exposed people actually develop the disease. Exposure does not always mean disease. A study done in Wisconin in the USA estimated that only 4 out of every 1000 exposed farmers developed the disease. This is probably because of different immune systems in different people's lungs. Bird Fancier's Lung is seen in people who keep or breed domestic birds, such as pigeons. Again, for reasons unknown, only a small number of exposed people actually develop the disease.

WHAT SYMPTOMS WILL I NOTICE?

Generally, 2 two different patterns of symptoms are noticed. The person may notice a sudden onset of symptoms a few hours after exposure to the offending dust, for example after forking hay. This pattern is known as acute extrinsic allergic alveolitis. The symptoms may include cough, shortness of breath, wheeze, fever and feeling generally unwell. This can happen on a regular basis before the person realises that there is a problem. The patient may recall that he does not experience any symptoms on days that he is not exposed to the hay or birds.
On the other hand, the patient may not have noticed any symptoms after exposure to the dusts, or ignored them as being unimportant. Then, over a period of months or even years, the patient notices a gradual onset of shortness of breath or cough. The symptoms may become gradually worse over time until the patient realises that something is wrong, and seeks medical help. Other symptoms may include weight loss and tiredness. This pattern is known as chronic extrinsic allergic alveolitis.

HOW IS IT DIAGNOSED?

The first test done is usually a chest x-ray, which shows abnormal shadowing in the lungs. Breathing tests are carried out to see how the illness is affecting the workings of the lungs. The breathing tests are performed in a special lung function laboratory in the hospital. When doing these tests, you will be asked to breathe in and out, through a mouth-piece. The air will enter a device that measures how well the "leaves" of the lungs are working. Blood tests will usually be needed. There is a blood test that can show if the person has been exposed to the offending dust. This is done by measuring antibodies to the dust. However, even if this comes back positive, it only proves that the person has had exposure to the dust. It is not enough to say that the person actually has the disease. The diagnosis of disease is based on breathing tests and x-rays. A special type of x-ray called a CT scan is usually done. This scan gives detailed pictures of the lungs that are better than ordinary x-rays. They show the inflammation or scarring in the lungs. Sometimes, a sample of your lung tissue needs to be sent to a laboratory for examination under a microscope. Lung tissue affected by extrinsic allergic alveolitis has a certain appearance when looked at under a microscope. This tissue sample (or biopsy) is obtained by passing a small tube down the nose or mouth, into your lungs. This is done while you are gently sedated with an injection. This procedure is called a bronchoscopy, and can be done as a day case. This is painless, and quite safe. The very rare complications that can happen will be explained. Less commonly, an operation under general anaesthetic may be needed to get the lung biopsy.

TREATMENT OF THE ILLNESS

Thankfully, extrinsic allergic alveolitis usually responds very well to treatment. Treatment is more effective in the early stages of the illness, when there is still inflammation in the lungs. In the later stages of the disease, the lungs may have become scarred. This scarring is less responsive to treatment. In many cases, it is simply enough to get the person to avoid the offending dust. This means the patient will be asked to stay away from the mouldy hay or birds. This is the most important aspect of treatment, and is often all that is needed. If the patient insists on staying in contact with the dusts, they need to wear a mask over the nose and mouth that filters out the dusts. However, this is not as effective as avoiding contact altogether. If the x-rays and breathing tests detect severe inflammation in the lungs, medication may be recommended by your doctor. The main medication used is steroid tablets . These tablets reduce lung inflammation, and prevent scarring. At first, quite a high dose of steroids will be given to you. The doctor will then reduce the dose slowly, and leave you on a lower dose of steroid for a given time period. Your doctor will decide what dose of steroid you need, and how long you will be on treatment. This decision is made by performing follow-up x-rays and breathing tests in the outpatient clinic. Unfortunately, steroids can cause unpleasant side effects, which your doctor will explain. Short courses of steroid treatment do not usually cause problems.
If the affected person avoids further contact with the offending dust, the outcome of treatment in extrinsic allergic alveolitis is very good. An exception is if the patient has had many years of heavy exposure to the dust and sought medical help very late. In this case, the lungs may have become irreversibly scarred, and therefore not as responsive to treatment. This is not usually the case.