Thinking in organ systems, disease types and acuity

There are thousands of diseases, but most of them can be described with a handful of labels: where in the body the disease lives, what kind of process it is, and how fast it unfolds. Those labels are more than filing categories. They compress a lot of information, and they are one of the fastest ways to narrow a list of possible diagnoses.

Three questions that describe almost any disease

1. Where? Which organ system, and which organs, are involved.
2. What kind? The underlying mechanism: infection, inflammation, a tumor, a blocked blood vessel and so on.
3. How fast? Whether it came on over minutes, days or years.

Answer those three and you have usually eliminated most of the possibilities.

Organ systems

Medicine is organized, in textbooks and in hospitals, around body systems. The main ones are:

Some diseases refuse to stay in one box. Systemic lupus erythematosus can affect the skin, joints, kidneys, blood and brain. Sarcoidosis can involve the lungs, skin, eyes and heart. Long-standing diabetes damages blood vessels, nerves, kidneys and eyes. Recognizing a multisystem pattern is itself a clue.

Disease types: the mechanism

The second label describes the underlying process. Common categories include:

• Infectious: caused by bacteria, viruses, fungi or parasites. Pneumonia, urinary tract infections and meningitis are examples.
• Inflammatory: the body's inflammatory response is the main problem, sometimes without infection, as in inflammatory bowel disease.
• Autoimmune: the immune system attacks the body's own tissues, as in type 1 diabetes, rheumatoid arthritis or Graves' disease.
• Neoplastic: abnormal growth of cells, from benign tumors to cancers.
• Metabolic and endocrine: problems with the body's chemistry or hormones, such as type 2 diabetes, gout or an underactive thyroid.
• Vascular: blocked, narrowed, leaking or ruptured blood vessels, such as a stroke, a heart attack or peripheral artery disease.
• Degenerative: gradual wear or loss of tissue over time, such as osteoarthritis or Parkinson's disease.
• Genetic and congenital: present from birth or caused by inherited variants, such as cystic fibrosis.
• Traumatic: caused by injury.
• Toxic and drug-induced: caused by poisons, alcohol or medicines.

Mechanism categories overlap too. An abscess is both infectious and inflammatory; a heart attack is vascular and causes an inflammatory response in the damaged muscle. Different textbooks draw the lines in slightly different places, which is worth remembering whenever a category feels like a close call.

Acuity: the time course

How fast a problem develops is one of the most useful clues in medicine.

• Acute conditions develop over minutes to days. Sudden onset, within seconds or minutes, suggests something vascular or mechanical: a burst or blocked vessel, a tear or a collapse.
• Subacute conditions develop over days to weeks, typical of many infections and inflammatory conditions.
• Chronic conditions persist for months or years, often defined as lasting more than three months. Slowly progressive problems suggest degenerative, metabolic or neoplastic causes.

Some conditions have a characteristic pattern over time: relapsing and remitting in multiple sclerosis or inflammatory bowel disease, or acute on chronic, like a sudden flare of long-standing lung disease.

How a disease is diagnosed and treated

Two further labels are useful for describing diseases, and both show up in Stat!'s Traits game.

How it is diagnosed. Some conditions are diagnosed mainly on the clinical picture: history and examination. Others need laboratory tests, imaging, a tissue biopsy, microbiology such as cultures, or genetic testing. Many need a combination.

How it is treated. Treatments include medicines, surgery, procedures such as endoscopy or catheter treatments, lifestyle changes, radiotherapy, and supportive care, which treats symptoms and supports the body while it recovers.

Putting the labels together

Here is how a few familiar conditions look when described this way:

Once you know two or three of these labels, the list of candidates shrinks dramatically. An acute, infectious, respiratory disease diagnosed with imaging is a very short list.

How Traits uses these labels

In Stat!'s Traits game, every guess shows six traits of the disease you named: system, type, acuity, organs, how it is diagnosed and how it is treated. Each trait is compared with the hidden disease and lights up green for an exact match, amber for a partial match or grey for a miss. The fastest way to win is to use early guesses to pin down the broad labels, such as system and acuity, then use the narrower ones, like organs and treatment, to choose between the remaining candidates. The Traits guide covers the rules and strategy in full.