6.03 Why diagnostic pathways?

Diagnostic pathways are based on the leading symptom. The patient usually shows several symptoms, from which the leading symptom is selected. Leading here does not mean the symptom with the most severe impairment of the patient. Some symptoms are so general that they are not leading. "General weakness" affects almost every sick person. Accompanying symptoms such as hair loss, difficulty swallowing or bleeding gums are more specific and lead further in the diagnosis.

Choosing the leading symptom is the first step on the path. If you get stuck, don't be afraid to go back and choose another one.

Which brings us to the second step on the path: what other symptoms are there and how do they relate to the main symptom? The combinations with a leading symptom can be varied, but they are finite. The "Medical history" section lists other symptoms that are associated with the main symptom. The analysis of the findings and the results of the physical examination are part of the further collection of data that can help us to weigh up the differential diagnoses.

Attempts to somehow arrive at the correct diagnosis from a leading symptom via an algorithm have not been particularly successful to date. The diagnostic path rejects this ambition: the path leads through a maze of possibilities, with many enquiries and assessments. The differential diagnostic approach is based on the idea that symptom complexes recur repeatedly and only allow a finite number of interpretations.

The conceivable interpretations are listed in section 4. They are organised according to the major pathogenetic principles - which cannot always be done consistently, but creates a little more order. The headings mean the following:

• Under "sympathetic" are diagnoses in which a leading symptom is involved but is not the leading symptom
• "Mechanical, traumatic" are illnesses caused by the effects of violence
• "Vascular" are diseases with a primary origin in the blood vessels
• Allergic" (inflammatory, without a known pathogen) includes diagnoses with immune reactions triggered in a variety of ways.
• "Inflammatory" all diseases caused by pathogens (viral, bacterial, fungal or parasitic)
• "Toxic, medicinal": toxic effects and effects or side effects of medicinal products
• "metabolic, endocrine"
• "chronic, degenerative"
• "neuromuscular"
• "Radiation"
• "Neoplasms"

In section 5, suggestions are made for an examination procedure. Some investigation methods often play a decisive role on the way to a diagnostic hypothesis: could the selected diagnosis be the correct one? What of what we have gathered speaks in favour of it? What speaks against it? Some diagnoses are immediately ruled out, others remain in the running. One of these will be the most likely.

In the final step, the diagnosis must be cross-checked: To do this, you must list the symptoms that are essential for making the diagnosis. Are these present? If something is missing - does this force a new diagnostic hypothesis? Or are there reasons why the symptom may be missing in this case? Does one of the targeted diagnostic procedures help?

Without a deeper understanding of the pathophysiology of the symptom, it will be difficult to make any progress. Such knowledge is a prerequisite. The notes in section 5.1 should therefore only contain brief reminders of the essential connections.

The structure of the diagnostic pathways is modelled on the CASE RECORDS OF THE MASSACHUSETTS GENERAL HOSPITAL, which are published weekly in the New England Journal of Medicine.

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