Interstitial Lung Disease

Interstitial lung disease is a family of conditions affecting the interstitium, the very thin layer of tissue that separates the air sacs from the blood vessels running past them. Oxygen crosses that layer with every breath. Inflammation, scarring or a mixture of the two thickens it, so less oxygen crosses and the lung as a whole becomes stiffer and harder to expand.

There are well over a hundred conditions in the group and they behave very differently. Some are driven mainly by inflammation and settle substantially when the immune response is damped down. Others are dominated by scarring, where the aim is slowing the process. Naming which one you have is therefore not an academic exercise, since it determines which of those two approaches is right and predicts what the coming years look like.

The causes include autoimmune and connective tissue diseases, inhaled organic material such as bird protein or mould, inhaled mineral dust at work, a number of medicines, radiotherapy to the chest, and a large group in which no cause is identified. Whatever the cause, the picture builds slowly over months, which is the usual reason it has been going on for a year before anyone investigates it.

Expect the first consultation to be mostly questions, and expect them to be specific. Every job and what was in the air, birds at home or on the balcony, feather bedding, damp walls and air conditioning, hot tubs, every prescribed and unprescribed medicine and herbal preparation, any radiotherapy, and the family history. This part identifies a treatable cause more often than any scan does.

Your doctor then looks for signs of autoimmune disease outside the lung, checking the joints for swelling, the skin and the hands for rashes, thickening and nail-fold changes, and the mouth and eyes for dryness. They listen at the lung bases for fine crackles and measure your oxygen at rest and after walking.

A high-resolution CT scan, breathing tests and a panel of autoimmune blood tests follow. In many centres the results are then discussed together by a chest physician, a radiologist and a pathologist, since a confident name comes from combining the three and not from any one of them. Sampling lung tissue is reserved for cases where that discussion cannot reach an answer.

The first thing to plan for is the time the diagnosis takes. Several weeks between the first appointment and a confident name is normal here, and it reflects the number of conditions that have to be separated. Your doctor may reasonably start treatment for the most likely cause while the workup continues.

Once treatment begins, judge it in months. Medicines that suppress the immune response are typically assessed at three months against the breathing test, the walking distance and the scan, and blood tests are done regularly in the meantime to watch for side effects.

Where an exposure has been identified, removing it completely is the step with the largest effect and it works on its own timescale, with improvement over months. A pulmonary rehabilitation programme of six to eight weeks improves breathlessness and walking distance whichever subtype you have. Reviews every three to six months continue indefinitely, and the trend across several of them is what your team treats.