Medical Reasoning vs. A Diagnostic Manual

 

I taught a course on medical decision making and how not to mistake a physical illness for a psychiatric disorder from about 1990 to 2002. The main theorists at the time were all internists – Stephen Pauker, Jerome Kassirer, Richard Kopelman, David Eddy, and Harold Sox.  I read their papers and attended their courses.  State-of-the-art in those days involved extensive differential diagnosis, Bayesian analysis, and an awareness of an extensive list of potential cognitive biases. I had been impressed with the need for pattern matching and pattern completion and incorporated all those elements into my course.  I eventually pared it down to about 9 sections in the lecture notes illustrated with case vignettes.

My original emphasis was to recognize that there are several considerations when assessing the medical aspects of psychiatric care.  The first is the medical stability of the patient.  Can they be cared for on a psychiatric unit or do their medical needs require medicine or in some cases surgery?  Do they need referral to a generalist of specialist?  This is more complicated than it sounds because the patient is there seeing a psychiatrist for what is supposed to be a psychiatric problem.  But that presentation is complicated by several factors including most patients have no primary care physician and no routine health care maintenance. Many will come into the emergency department concerned about a medical problem but get sent to psychiatry. In that situation, people still get all of the acute medical illnesses including heart attacks, strokes, asthma attacks, pulmonary emboli, seizures, pneumonia, meningitis, encephalitis, and acute cholecystitis to name a few.  Many exhibit non-specific behaviors like agitation, crying out, aggression, or unresponsiveness that can be due to either a psychiatric disorder or a medical problem.    

The second is a psychiatric presentation of a physical illness in a communicating patient. The classic presentations involve brain pathology that is infection, inflammatory, vascular, trauma, or neurodegenerative.  Systemic endocrinopathies and inflammatory disorders are a close second. 

Finally, there is the patient with a clear psychiatric disorder who has intercurrent illness that is or is not known.  Examples that I have seen many times include current or new onset diabetes mellitus, profound anemia usually secondary to an upper or lower GI bleed, dermatology conditions that have often been neglected, symptomatic nutritional deficiencies (B12, folate, D), sexually transmitted diseases, complications of substance use like cirrhosis, and various acute and chronic infectious diseases.

Given that large population with diverse medical and psychiatric problems as well as diverse presentations that can include denying any physical problems – I typically reviewed how the diagnoses occurred.  Pattern matching was the fastest.  The physician has seen a physical finding, lab, behavior, etc – many times before, knows what it is, diagnoses it and treats it.  A good example is a rash.  Dermatologists are rash experts and can correctly classify rashes and marginal cases much faster than primary care physicians (4).  The same is true for diabetic retinopathy and ophthalmologists (5).  Until you have seen a person with severe mania or catatonia, neuroleptic malignant syndrome, or serotonin syndrome it is less likely that you can diagnosis the conditions by reading criteria in a book.  Patterns are important for all medical specialists.

On the other end of the spectrum is the contemplative side of diagnosis.  There are several possible diagnoses, and it takes additional data, thought, and reasoning to come to a final diagnosis. Every medical student does this in their initial internal medicine rotation.  There is encouragement to produce a list of many diagnoses that might account for the presentation – but even as the case is being recorded or presented that list rapidly narrows to the apparent diagnosis.

In psychiatry, it may take much more data and collateral information to make a specific diagnosis at the initial presentation.  First episode psychosis (FEP) is a case in point. It is very important to determine what the symptoms onset was like and whether there were any associated mood symptoms or substance use problems. The patient may not be able to describe the phenomenology and depending on the circumstances treatment may be initiated while to diagnostic process is ongoing.  Teaching about the diagnostic process, we would spend time discussing what that might look like combined with a recursive approach to the patient and an awareness of cognitive and emotional biases.  I provided several examples of non-psychiatric physicians making errors due to emotional biases.

Since my course, the literature on medical decision making has changed to some degree.  There is some literature that addresses expertise in general at both the level of cognitive psychology (1) and neurobiology (2).  The general approaches have been to analyze expertise and diagnostic reasoning from the perspective of typical domains (cognitive, perceptual, motor) or to look at a general model and how that has developed over the years.

A dual processing model (3) is generally considered the best current representation of clinical reasoning and decision making.  In this model, there is a fast automatic, heuristic, and unconscious system called Type 1 and a slower conscious, analytical, and effortful system called Type 2.  Additional properties are indicated in the following table.

Parameter	Type 1	Type 2
Speed	Fast, automatic, unconscious/preconscious, little effort	Slow, deliberate, analytical, varying degrees of effort
Control	Minimum control, similar to automatic associations in everyday life except more focused	Control over thought process and direction
Systems and Processing	Pattern recognition and completion, implicit learning, access to long term memory	Working memory and manipulation of data in working memory, planning and reasoning based on that data
Memory Systems	Long term memory	Short term and working memory
Localization	-Orbitofrontal cortex (OFC) -Basal ganglia (caudate, putamen) -Insula -Anterior cingulate cortex -Amygdala -Hippocampus	-Dorsolateral prefrontal cortex (DLPFC) -Left inferior frontal gyrus -Middle frontal gyrus -Inferior parietal lobule -Precuneus -Hippocampus

 A clinical example of Type 1 reasoning is when a trained clinician recognizes a classic presentation of a medical illness, diagnosis, or finding.  An example I frequently use is when one of my Infectious Disease attendings who was an expert in Streptococcal infections recognized characteristic rash from across the room on a patient we were consulted for a different problem.  He made the diagnosis within seconds and told us how it could be confirmed.  In studies of the process the orbitofrontal cortex and limbic connections are activated.  Training is a critical element, especially seeing a maximum number of patterns and their variations.  Although the characterization is that this is a fast and automatic process, there is some room for deliberation.  For example, recognizing or attempting to classify equivocal cases without classic presentations. 

Type 2 reasoning is considered more of the typical process of differential diagnosis.  The findings are compared, analyzed, and accepted or rejected based on additional data and clinical judgment. This process is thought to localize in dorsolateral prefrontal cortex (DLPFC) the home of the working memory where data can be maintained and analyzed.  The left inferior frontal gyrus contributes to rule-based reasoning and hypothesis testing.  A clinical example from my experience is the case of the agitated stuporous patient.  These cases require a great deal of caution because they are most likely to represent a serious or life-threatening illness.  It requires a clinician who knows how to examine patients with stupor or coma and rapidly makes sense of the history and findings. It is a problem that can rarely be solved by Type 1 reasoning alone due to a fairly non-specific presentation.  Some of the critical points for hypothesis testing will be signs of increased intracranial pressure, purposeful response to painful stimuli, eye movements, reflex and musculoskeletal exam abnormalities, signs of infection, and meningeal signs.

The interaction between Type 1 and Type 2 systems is not necessarily sequential but it can be with the Type 1 system matching patterns that lead to hypothesis generation.  There is some evidence that in most clinical situations most of the diagnoses occur with Type 1 reasoning.  Experts can operate at the level of Type 1 reasoning due to extensive experience.  There is not necessarily a hard separation based on the properties in the table. Some hypothesis testing can occur at both levels.  Both systems are commonly grounded in both the limbic system and the hippocampus.

The human brain is capable of parallel distributed processing of data or information.  This means that there are many processing areas in the brain that are interconnected and they can all be working at once.  The modern conceptualization is brain networks that are active processing areas connected by white matter tracts widely distributed through the brain.  

That brings me to my model of diagnostic reasoning (see lead graphic and click to enlarge).  It is based on the course I taught, neuroanatomy and neurology, and what I have observed clinically. When I was talking about pattern matching 20 years ago based on my observations and reading studies in dermatology, ophthalmology, radiology, and pathology – the term seemed to fade rapidly from the diagnostic reasoning literature.  It was revived somewhat by the more recent focus on AI and comparison of that modality to humans.

There was a lull in Bayesian analysis after the invention of computerized programs like Quick Medical Reference (QMR) and Iliad.  They were designed to facilitate medical diagnoses by providing an exhaustive list of findings and their probabilities. These were 20^th century personal computer programs and not AI.  A study of these and 2 additional programs suggests that these programs got 52-71% of 105 diagnostic cases correct with 19-37% being the mean portion of correct diagnoses (6). Despite those figures the programs provided an additional 2 diagnoses per case that experts considered as relevant.  The authors recommended that the programs be used only by physicians who could include the relevant and exclude the irrelevant information provided by the programs.  The programs were discontinued without further modification or updates.  

That is the 8-mile-high view.  I could do a deeper dive into the neuroanatomy and neurophysiology.  But the clear reality of the situation is the ability to make a psychiatric diagnosis resides in the brain of a psychiatrist and not a classification manual or a checklist.   Manuals and checklists are crude approximations of some of the cognitive features that psychiatric experts possess.  Like all experts – skill will vary based on practice, exposure, and interest because of the effects on these brain systems.  But we are well past the point of equating what a psychiatrist does to a crude manual.  A manual never saved or treated anyone.  Further – the diagnostic reasoning process emphasizes elements that are important for education and training. It seems that in the past decades there has been a preoccupation with evidence-based research rather than the evidence itself. It does not do the physician or patient any good to be in a situation where that physician is unable to communicate with a person who is in a critical state and has no idea how to assess that problem.  Rearranging diagnostic criteria in a manual for the ninth or tenth time does not get you there.   

 

George Dawson, MD, DFAPA

Supplementary 1:   Before anyone says the diagram is too complex - it is a general diagram for any human diagnostician.  The main modifications for physicians and psychiatrists are the interactive aspects that include empathic comments, formulations, and numerous verbal interventions that other diagnosticians may not need to use.             

 References:

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1:  Bilalić M.  The Neuroscience of Expertise.  Cambridge University Press. Cambridge, United Kingdom. 2017.

2:  Maguire EA, Gadian DG, Johnsrude IS, Good CD, Ashburner J,  Frackowiak RSJ, Frith CD. 2000. Navigation-related structural change in the hippocampi of taxi drivers. Proc Natl Acad Sci USA 97:4398–4403.

3:  Norman GR, Monteiro SD, Sherbino J, Ilgen JS, Schmidt HG, Mamede S. The Causes of Errors in Clinical Reasoning: Cognitive Biases, Knowledge Deficits, and Dual Process Thinking. Acad Med. 2017 Jan;92(1):23-30. doi: 10.1097/ACM.0000000000001421. PMID: 27782919.

4:  Federman DG, Concato J, Kirsner RS. Comparison of dermatologic diagnoses by primary care practitioners and dermatologists. A review of the literature. Arch Fam Med. 1999 Mar-Apr;8(2):170-2. doi: 10.1001/archfami.8.2.170. PMID: 10101989

5:  Sussman EJ, Tsiaras WG, Soper KA. Diagnosis of Diabetic Eye Disease. JAMA. 1982;247(23):3231–3234. doi:10.1001/jama.1982.03320480047025

6:  Berner ES, Webster GD, Shugerman AA, Jackson JR, Algina J, Baker AL, Ball EV, Cobbs CG, Dennis VW, Frenkel EP, et al. Performance of four computer-based diagnostic systems. N Engl J Med. 1994 Jun 23;330(25):1792-6. doi: 10.1056/NEJM199406233302506. PMID: 8190157.