Interstitial lung disease

What it is

Interstitial lung disease is swelling or scarring of the tissue between the air sacs of the lung. That tissue has a name, and it's called the interstitium. It's where oxygen crosses from the air you breathe into your blood, so when it swells or scars the lung stiffens and that crossing gets harder.

So the symptoms of it aren't what most people would expect from a lung problem at all. There is no pain to speak of, which throws people. What there is instead is breathlessness, usually on effort before anything else, and a dry cough that won't settle down.

Why it decides the outlook

This is why the lungs get checked rather than waited on, and the survival figures are the reason. The German study of 3257 people gives the clearest comparison. Five-year survival was 96.4 percent in those with no lung involvement at all, survival differed significantly across the groups, and it was worst in those who had both lung disease and pulmonary hypertension together.

Three things in that study were associated with lower death rates. Being female came with a hazard ratio of 0.3, a higher body mass index with 0.9, and better gas transfer on lung testing with 0.98. The gas transfer figure is the one a clinic can watch over time.

One study followed 114 people with myositis-related lung disease, where all-cause mortality was 27.2 percent. Four things predicted death in that group on their own. They were an acute or subacute course, a lower forced vital capacity, age, and a clinically amyopathic diagnosis rather than polymyositis.

Which diseases cause it, and how often

Several autoimmune diseases cause it, and they do it at very different rates. Those differences are worth knowing, because the number that applies to you depends on which diagnosis you have. One Korean study reviewed 751 people with systemic sclerosis, where interstitial lung disease was the most common organ problem at 52.7 percent. Reflux came next at 32.9 percent, and pulmonary arterial hypertension at 13.6 percent.

One German study followed 3257 people with systemic sclerosis, where it was present in 34.5 percent at the start. By the end of follow-up that had reached 47.6 percent. Another 15.2 percent had it alongside pulmonary hypertension, and 6.5 percent had pulmonary arterial hypertension without it.

One Portuguese study followed 198 people with inflammatory muscle disease, and 34.8 percent of them had interstitial lung disease. In antisynthetase syndrome the figure is higher still. One Chinese study of 88 people with that syndrome found lung disease in 90 percent of them, which made it the most common feature of the illness, ahead of the muscle involvement it's named for.

The fast-moving form

Most interstitial lung disease develops over years, and a minority worsens over weeks. That second form is where the risk concentrates. In that study of 114 people the disease was acute or subacute in 59 of them and chronic in 55, and survival was much lower in the acute or subacute group, at P under 0.001.

One review went looking for what predicts it. It pooled 27 groups of people with dermatomyositis, holding 2579 people between them, of whom 620 had the fast-moving form. Lactate dehydrogenase separated the groups most clearly, at a mean difference of 75.94 whose true value the study puts between 64.20 and 87.67, at P under 0.00001.

Two other tissue damage markers came out much weaker than that. Aspartate aminotransferase came out at 24.35, with the true value ranging from 8.74 to 39.96. Alanine aminotransferase came out at 26.20, from 10.04 to 42.36.

Two clinical predictors was notable from the rest. Fever came with an odds ratio of 3.16, from 2.12 to 4.72. A positive anti-Ro-52 came with 2.87, from 1.52 to 5.40, and fever is the one a reader can notice for themselves.

The scan pictures

The picture on a scan holds information, and the two names below are worth recognizing. They'll appear on your own report if you have one. Non-specific interstitial pneumonia is the most common of them in this setting, and one study of 103 people with anti-Jo-1 antibodies found it in 52 percent.

Next came that picture overlapping organizing pneumonia, at 22 percent, and restriction on lung function testing was present in 98 percent. One study of 198 people with inflammatory muscle disease found that picture leading too. Non-specific interstitial pneumonia was there in 69.5 percent of those with lung disease, so one picture dominates in both groups.

Which antibody you have changes what the scan shows. One study looked at 108 people with antisynthetase syndrome and lung disease, where organizing pneumonia led in the anti-EJ group at 78.2 percent. That beat the anti-PL-7 group at P under 0.001 and the anti-PL-12 group at P equals 0.025.

What usually happens

The studies here point more toward stability than toward decline, and that's worth saying beside the survival figures. Both of those things are true at once. That Portuguese study of 198 people found most scan pictures stayed stable, at 89.6 percent, with gas transfer improving over follow-up at P equals 0.022.

Forced vital capacity was stable or improved, at P equals 0.097, which doesn't clear the usual threshold. One study re-examined 34 people with myositis-associated lung disease after more than a year, finding 26 stable and 8 deteriorating. Six of the deteriorating group needed home oxygen. Two things predicted that decline on their own, which were a positive anti-PL-7 test and a lower percent predicted forced vital capacity.

One study of 108 people with antisynthetase syndrome and lung disease reports no deaths at all. The median follow-up there was 10.7 months, which is a short window and worth reading as one. So the honest summary of all this comes in two halves. This is a serious complication in which most people are stable on treatment, and the fast-moving form is a different situation with different numbers.

Common misconceptions.

Related terms.

• Amyopathic dermatomyositis, where the fast-moving form is most common.
• Antisynthetase syndrome, where lung disease reaches 90 percent.
• Systemic sclerosis, where it's the most common organ problem.
• Pulmonary hypertension, the other lung problem these diseases cause.