RESTRICTIVE LUNG DISEASES

Hard to breathe in

Restrictive Lung Diseases are a group of lung problems defined by low lung volumes. They have difficulty breathing in. They are more rare than the obstructive diseases. In all of these disorders, all of the measured lung volumes will be smaller than in healthy lungs. However, the FEV1:FVC ratio is normal or elevated.

There are two major categories of RLDs. One has a normal DLCO (Diffusing capacity of the Lungs for Carbon monoxide), and the other has a low DLCO. The DLCO is a fancy pulm test that essentially measures the thickness of the points where the alveoli meets the pulmonary capillaries (where gas exchange occurs).

Mechanical RLDs have a normal DLCO and normal AA gradient. What I mean by mechanical is that their lungs are perfectly healthy, but their muscles struggle to take a deep breath in. The three best examples of this are Myasthenia Gravis, oversedation (opioids) and obesity.

Fibrotic RLDs have a low DLCO. In all of these diseases, there is too much fibrosis (scarring) of the lung tissue. The excess connective tissue displaces any available space for air, and makes the lung less stretchy which makes it hard to inhale. There are a LOT of causes, and some of the finer pathophysiological mechanisms are still being explored. Examples include Idiopathic Pulmonary Fibrosis (30%), Pneumoconiosis (occupational exposures) (25%), Sarcoidosis, Drug toxicity, Vasculitis, Pulmonary Langerhans Cell Histiocytosis and Hypersensitivity Pneumonitis.

Flow Volume Loops

PNEUMOCONIOSIS

Dust disease

Pneumoconiosis is any lung disease caused by inhalation of fine mineral dust. In the lungs, fine dust is eaten by the aptly named dust cells (medium dust is cleared by cilia and large dust by coughing). Pneumoconiosis is really easy to spot, because these are almost always caused by weird industrial jobs. If a test question mentions a construction worker, shipyard worker, NASA engineer or coal miner, they’re trying to tell you something. And although I don’t think this is very important, just keep in mind that Pneumoconiosis is especially bad if you already have Rheumatoid Arthritis. Their lungs fill up with rheumatoid nodules. It’s called Caplan Syndrome

Coal Miner Lung is pretty self explanatory. It’s also called Black Lung. Carbon dust is surprisingly safe (as far as mineral dust inhalation goes). It takes a lifetime of heavy coal mining (without protective equipment) to get it. But the Black Lung causes cripping restrictive lung disease, characterized by progressive massive fibrosis and an abundance of large fibrotic balls.

Berylliosis is caused by burning Beryllium (a metal stronger than steel and lighter than aluminum). If a vignette mentions the aerospace industry, it’s Berylliosis.

Silicosis is the most common pneumoconiosis. It’s due to the inhalation of pulverized quartz dust, otherwise known as silica. While quartz is a pretty boring rock, silica is one of the most catastrophically destructive substances your lungs could ever touch. It’s an important part of concrete. It’s also basically sand, so sand-blasting is a big risk factor. Not Fun Fact - the largest industrial disaster in US history, the Hawk Nest Tunnel Disaster, was due to silicosis. During the Great Depression hundreds of largely black men were forced at gunpoint to dig a tunnel. Masks were not permitted. Many (if not all) of them developed fibrotic lung disease. The death toll is debated, but likely in the hundreds.

Asbestosis is due to the inhalation of asbestosis, a shockingly effective insulating material. But it’s damn toxic. It’s still found in old houses and old ships. It hits the lower lobes, just above the diaphragm. Almost everyone exposed to asbestosis develops non-cancerous pleural plaques. But some get cancer. Asbestosis is basically the only cause of mesothelioma, but since mesothelioma takes 25 years to develop, and regular lung cancer takes only 10 years, actually the most common lung cancer with Asbestosis is regular lung cancer (this is SO high yield). Also look for Ferruginous bodies on histology of a lung lavage. These are some of the most unique findings in all of histology-land. They’re basically asbestos fibers coated with iron. They look like little dumbbells.

Fun Fact - Pneumonoultramicroscopicsilicovolcanoconiosis is caused by volcanic ash. It’s the longest word in the English language with 45 letters.

LUNG FIBROSIS

Scarred lungs

Idiopathic Pulmonary Fibrosis (IPF) is the most common cause of restrictive lung disease. As the name suggests, the lungs fill up with scar tissue, but we don’t know why. I encourage you to check out some of the latest research on IPF, there’s been a lot of recent advancements. It’s likely due to a combination of bad genes and a harmful environmental exposure (like air pollution). Like other restrictive lung diseases, it can cause dyspnea, a dry cough, clubbing and cor pulmonale. On auscultation you can hear fine crackles. You can diagnose it based on a chest CT that shows lung honeycombing. IPF has a sinister timeline. It steadily worsens and is usually fatal after a few years. There is no cure, other than transplantation. There are some promising new treatments like Pirifedone (TGFb inhibitor) and Nintedanib (TK inhibitor) that seem to slow fibrosis.

Cryptogenic Organizing PNA is a specific kind of IPF. It’s a rare complication that happens shortly after a bout of PNA (see the PNA page, specifically at phase 4 of the cartoon). The alveoli are flooded with interstitial fluid (to drown the bugs). After the bugs die, the fluid is drained by macrophages. Sometimes (and we’re not sure why) fibroblasts manipulate the fluid instead. They don’t drain the fluid, but instead replace it with collagen. You can see how this is essentially the “opposite” of regular IPF -- the alveoli are filled from the inside, instead of the walls growing into the cavity. On CT, there will be sporadic fibrosis. On histo, you see random bouts of fibrosis, with normal alveoli scattered around.

Hypersensitivity Pneumonitis is sort of like febrile asthma that is triggered by “organic antigens,” like animal proteins or mold. It’s especially common on the farm. It’s sometimes called Pigeon Breeder Lung. Like asthma, it is intermittent, starts suddenly and involves eosinophils. It turns out that aerosolized animal feces is bad for the lungs. It triggers a granulomatous and eosinophilic interstitial lung injury. It can be seen on a chest x-ray as bilateral interstitial opacities. Chronic recurrent exposure can lead to pulmonary fibrosis.

Medicines that hurt the lungs: Amiodarone, Bleomycin, Busulfan, Methotrexate, Cyclophosphamide, Nitrofurantoin. Both Rheumatoid Arthritis and Methotrexate (the treatment for RA) can cause restrictive lung disease. Also, radiation therapy.

SARCOIDOSIS

Sarc- (flesh) -oid- (like) -osis (disorder)

Sarcoidosis is a mysterious (and common) auto-immune disease that likes to attack the lungs (restrictive lung disease), but can involve nearly every organ. The immune system goes haywire in response to some unknown antigen or mutation, resulting in non-caseating granulomas appearing all over the body. Although we don’t know the cause, Sarcoidosis most often affects young adult Black women. This is a diagnosis of exclusion, one that is typically made using a biopsy. It often resolves on it’s own, but can rarely be fatal. Regardless, the treatment mostly consists of steroids.

So lots of small nodules form throughout the body. It can involve nearly any organ. But most often hits the hilar lymph nodes. Immune cells gather in the hilums, eventually coalescing into bundles called granulomas. Bilateral hilar lymphadenopathy can be spotted on chest XR or CT. It’s usually asymptomatic, but can cause a boat load of symptoms in many different organs. Like most autoimmune diseases, it will cause some fever, chills, fatigue, weight loss, erythema nodosum (painful red lumps on legs) and uveitis.