Pneumonia is one of those medical conditions that is constantly thrown around without being rigorously defined—and as we all know by now, rigor is absolutely paramount in my view of academic medicine and medical etymology. Let’s start by looking at the word from an etymological standpoint:

Origin: Greek, pneumon (lung) + –ia (condition of)
Condition of the lung

Well, that certainly wasn’t very helpful—at least not at first glance. There can be many conditions of the lung that are called “pneumonia” and the classic case of a lung infection is merely one of them. Compare pneumonia to pneumonitis:

Origin: Greek, pneumon (lung) + -itis (inflammation of)
Inflammation of the lung

There are many inflammatory conditions of the lung, but only a few of them are called “pneumonitis” because pneumonitis is considered to be inflammation of the lung tissue itself (the lung parenchyma). There are some who then consider pneumonia to be inflammation of the air sacs in the lungs (the alveoli). This makes sense for the most part; the bacteria, viruses, fungi, and parasites that can cause pneumonia would cause alveolar inflammation.

lung diagram

To put things in perspective, when somebody is admitted to the hospital for pneumonia, the classic picture is someone who acquires a bug, and said bug colonizes the alveolar space. The resulting “mass” that forms (usually in one lobe of the lung) is called a consolidation:

Origin: Latin, con- (with) + solidus (solid)
With solid, i.e., things that aggregate to form a “solid”

For these “classic” pneumonias, we can call them community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), and the like. Some bugs associated with the former are things like Streptococcus pneumonia and Pseudomonas aeruginosa, and some bugs associated with the latter are things like Staphylococcus aureus and Haemophilus influenzae. (Stay posted for microbiological etymology!)

But it turns out that this isn’t the whole picture. Pneumonia is indeed as general as its etymology suggests, for there can be inflammatory and fibrotic conditions of the lung—and both classes can fall under the term “pneumonia.” (Generally, inflammation is caused by the infiltration of white blood cells and fibrosis is caused by the production of excess connective tissue, e.g., collagen.) Thus, as a counterexample to the definition that pneumonia is simply the inflammation of the alveoli, we have something called usual interstitial pneumonia (UIP). It is a form of interstitial lung disease in which the tissue between the alveoli is fibrosed with collagen.

uip ctThe classic “honeycomb lung” appearance of UIP on CT scan

To end this post, I posit my generalized definition of pneumonia: pneumonia is a principally inflammatory or fibrotic condition of the lung. By formalizing this definition of pneumonia, I am faithful to the etymology and make pneumonitis a subset of pneumonia. Note that I use the word “principally” in front of inflammatory—the reason why is that cancers of the lung can cause inflammation, but cancers are not considered to be pneumonias by any definition or practice.

In another post I will discuss the classic methods of diagnosing “normal” (generally bacterial) pneumonia and the etymologies of these techniques. Here is a small teaser: one of the terms involves the Greek word for goat! Can you guess which one? Leave a comment below.

What on earth is pyelonephritis? Let’s understand what it actually is by taking a look at its etymological breakdown.

Origin: Greek, pyelos (basin, taken to mean pelvis) + nephros (kidney) + –itis (inflammation of)
Inflammation of the basin and the kidney

At first, this seems cryptic. What does basin refer to, and what exactly does kidney refer to? Starting with the root pyelo-, it denotes “pelvis,” but its base etymology comes from the Greek pyelos (basin). There is in fact such a thing as pyelitis, which would be inflammation localized to the renal pelvis. As for the nephr- root, it of course means kidney, but to be more precise, it refers to the kidney parenchyma. Nephritis on its own denotes the inflammation of the kidney’s functional tissue.

kidney anatomy rev

At the end of the day, pyelonephritis is the joint inflammation of the renal pelvis and the renal parenchyma. A vast majority of the cases are caused by a bacterial agent such as E. coli., and as such, they proliferate in a large portion of the kidney instead of being localized to only the pelvis or the parenchyma.

There are three types of pyelonephritis: acute, chronic, and xanthogranulomatous. Let’s look at the last one:

Origin [1]: Greek, xanthos (yellow)
Origin [2]: Latin, granum (grain) + –ula (diminutive) + –oma (mass/proliferation/tumor)
Forming yellow granulomas

Indeed, under the microscope, one would find granulomas—collections of macrophages that try to wall off infections they cannot eradicate. On gross appearance, these granulomas appear yellow because they are macrophages that have been filled to the brim with lipids.

xantho rev

In colloquial language, we often append the suffix ­-itis to a word to denote a disease or condition of said word. It is in effect an indication of an unhealthy amount of something either abstract or tangible. If someone is being lazy, we can say that he or she has come down with a case of lazyitis. Too much time in front of a computer can afflict you with a nasty case of computeritis. At its roots, –itis means “pertaining to” in Greek, so in some sense, this colloquial use of the suffix is the most faithful to its base etymology.

In more technical language, –itis is used as a medical suffix, and it simply denotes “inflammation of.” I can’t tell you how many times I have heard people use ­–itis to immediately denote “infection of.” Let’s list some examples.

Origin: Neo-Latin, appendix (something appended, in this case to the colon) + -itis (inflammation of)
Inflammation of the appendix

Origin: Greek, byrsa (hide/skin) + ­-itis
Inflammation of the bursa (a pouch or sack that facilitates motion, e.g., suprapatellar bursa)

Origin: Greek, chole (bile) + kystis (bag) + -itis
Inflammation of the gall bladder (which stores bile)

Yes, many times, these conditions come about from infection by a bug that isn’t supposed to be there. But there are many other causes of inflammation, such as:

  1. Trauma
  2. Autoimmune reaction
  3. Drugs
  4. Burns
  5. Radiation

So the next time someone mentions an ­–itis, always remember that the inflammation of the target organ can be caused by something other than infection. If you wish to convey the fact that an inflammation of the appendix is caused by an infection, you can prepend the word with “infectious,” to make it an infectious appendicitis. Or if you are more certain of the cause of this infection, you can use a bacterial/viral/fungal modifier, for a bacterial appendicitis. For a non-infectious cause, you could say the cause for an inflammation of the liver is a drug-induced hepatitis.

Finally, if someone mentions a type of ­­itis that you are not familiar with, use the word itself to help you out. I remember hearing the term bronchiolitis last year when learning about COPD (chronic obstructive pulmonary disease). I didn’t know what bronchiolitis was until I stopped for a second to think about it: the inflammation of the bronchiole(s). Contrast this with bronchitis, which is the inflammation of a main stem bronchus.

lung anatomy rev

So, given this, let me know in the comments what these terms are and what their most common causes are:

  1. Cholangitis
  2. Colitis
  3. Pneumonitis
  4. Endocarditis
  5. Vasculitis
  6. Phlebitis
  7. Gastroenteritis