Pathology

Classifications

Classification systems can aid learning but can also lead to fundamental insights. Disease can be classified by:

1. Alphabet (A-Z)

2. By body system or life cycle & related specialty

3. By aetiology (cause)

Some conditions are simple: basal cell carcinoma is both dermatologic body system, cancerous aetiology, predominantly adult life stage, affects the skin and is managed by dermatologists. However many conditions have overlap: pulmonary embolus is the respiratory, vascular and haematopoetic body systems (arguably), of multiple aetiology (cancer or chronic infection is one)

There is frequently overlap between conditions

Alphabetical

My personal favourite classification system for its ability to facilitate multisystem disorders. 

Issues include multiple names e.g. GPA and Wegner's and a number of small terms cholecystitis, choledolithaisis etc that I group under biliary stone disease. 

Go to AZ Disease

Body Systems

The 12 body systems & specialties involved

Body System  

1. Nervous

   1. 1. Neurology

      2. Psychiatry

      3. Neurosurgery

2. Endocrine

   1. 1. Endocrinology

3. Senses

   1. 1. Ophthalmology

      2. ENT

4. Cardiovascular

   1. 1. Cardiology

      2. Cardiothoracic

      3. Vascular

5. Respiratory

   1. 1. Respiratory 

      2. Cardiothoracic

6. GI

   1. 1. Gastroenterology

      2. General Surgery

7. Urinary

   1. 1. Renal

      2. Urology

8. Reproduction female

   1. 1. Gynaecology

9. Reproduction male

   1. Urology

10. Haematopoietic

    1. Haematology

11. Musculoskeletal

    1. Orthopedics, 

    2. Rheumatology

12. Skin

    1. Dermatology

Connective tissue

Multisystem disorders

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Life Cycle

1. Baby & child: obstetrics, neonates, paediatrics - infections, injuries, genetic

2. Adult Medicine: internal medicine, surgery etc- infections, trauma, environmental

3. Elderly: medicine of the Elderly- infections, cancer, cardiovascular disease

4. End of life: palliative care: cancer, neurological disorders

*

Aetiology (by cause)

Causes of disease:

13. Cancer and growths

14. Environment (acute)

    2. 2. 1. Infections

          2. Trauma (physical, chemical, emotional)

          3. Toxicology

15. Genetic

    2. 2. 1. Congenital

16. Everything else

Defining Diseases and Syndromes

Medicine follows the problem -> solution schema. Disease is the medical definition of a 'problem' which shares a common 'solution'. It is often helpful to further classify disease diagnoses by aetiology and severity. The body's immune system often recognises a disease and elicits an immune response. 

 E.g. most pneumonia's require antibiotics and be further classified by organism and severity by mortality using the CURB-65 score. The definition of disease is not straightforward and can rely upon societal and philosophical principles. 

Disease characteristics

• Causes a 'problem'

• Often elicits an immune response. 

Syndrome: constellation of symptoms 

For example Down Syndrome is preferably thought about as a syndrome within the context of neurodiversity. Neurodiversity states that not all individuals must align and that it is normal for a society to have a diverse range of personalities. For example being in the top 5% of height deciles isn't a disease, however there would be higher rates of disease here, for example acromegaly. Neurodiversity also applies to ADHD and autism spectrum disorder. In the case of neurodiversity, individuals may find the idea that there is a 'problem' validating, however labelling this lifelong syndrome as a disease can feel insulting at times. 

Medical Schema

The common medical schema is below: 

• Symptom -> sign -> diagnosis -> classification (aetiology/ severity)

• Symptom: information subjective to patient, e.g. headache

• Sign: objective detail gathered by doctor e.g. meninginism, hypotension, raised CRP

• Diagnosis: dictation of management, e.g. meningitis, subarachnoid haemorrhage

• Classification

  • Aetiology: streph pneumonia meningitis

  • Severity: e.g. 30d mortality score dictating disposition

Some of the pages in AZ disease are signs, e.g. anaemia but the majority are disease, e.g. Colorectal Cancer. It is helpful, where possible to fully categorise the diagnosis to standardise management.

It is worth knowing the rough sensitivity and specificity of each sign for each disease, e.g. a d-dimer is highly sensitive but poorly specific for a PE. 

Page written in 2024.