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.

Adding Rather than Subtracting Bias - An Underlying Basis for Polypharmacy?

There was an interesting piece in Nature this week (1,2) about cognitive biases in complex problem solving.  The research psychologists asked subjects to solve problems of varying complexity and structure from the perspective of whether additional structures or steps were necessary or whether an optimal solution could be obtained by subtracting structures or steps. I will briefly describe each of the problems in the table below (pending permission to use one of their graphics).

Task	Description
Abstract grid task	Transform a grid pattern to make it symmetrical
Suggested changes to a large public university	Changes to improve the sense of community, enable student learning, and prepare students for a lifetime of service
Lego block structure	Improve the 8 or 10 block structure
Lego block structures	3 possible structures built from 12 blocks of a pool of 24 blocks on a 6” x 8” base.
Lego block structure	Revision of original structures made from a possible 20 blocks to make a 10 block structure
Lego block structure	Modify a Lego structure so that it can hold a brick over the head of an action figure in the structure
Read and summarize an article	Make a 6-8 sentence summary and then edit it to a shorter version
Read and summarize an article	Edit someone else’s summary and edit it to “omit needless words”
Day trip to Washington DC	Inspect a trip itinerary and suggest changes to improve it
Make a grilled cheese sandwich	Make a grilled cheese from 27 ingredients -
Modify a soup recipe	From 5, 10, and 15 ingredient soup recipes – modify from a list of ingredients and modify to improves the soup.

Inspection shows that the cognitive tasks cover many domains ranging from 2D and 3D visuospatial tasks, language tasks, and more theoretical tasks that involve speculative rather than confirmed outcomes. The authors suggest an all-encompassing definition: “the cognitive science of problem solving describes iterative processes to imagining and evaluating actions and outcomes to determine if they would produce an improved state.”(p. 258).  They define subtractive transformations as fewer components than the original and additive transformations as more components than the original.  The authors noted a bias in anecdotal literature to making conscious subtractive transformations and that suggested to them that strategy may be less common or undervalued. 

Across all experiments, the tendency toward subtractive strategies with the general instruction were lower but probabilistic.  For example, across all experiments, subtractions ranged from 21-41%.  A second set of conditions with subtle subtraction cues increased the rate of subtractive transformations to 43-61% across the same experiments.  At one point the researchers added a cognitive load task that was basically a distractor to use more attentional resources. In these conditions cognitive shortcuts are less accessible. Under those conditions subjects failed to identify a subtractive solution more frequently.  The authors also studied subjects form Germany and Japan suggesting that there is cultural generalizability of the additive over subtractive strategies.

The authors consider that the differences could be accounted for by generating a number of additive and subtractive ideas and selecting the additive or they simply default to the additive.  They elected to look at the default to the additive mode. They describe heuristic memory searches allowing for the timely access of relevant information.  They suggest a number of reasons what additive strategies may be favored including – the processing may be easier, semantic biases such as more being better, cognitive biases may favor the status quo or less change, and it may be more probable that additive rather than subtractive changes offer a better outcome.

This is an interesting paper from a number of perspectives.  First, it presents a cognitive psychology approach with no purported biological mechanisms. There are no functional imaging studies or brain systems described.  The theories and design of experiments depends on a psychological model of cognitive function. Second, the model is probabilistic.  Although the title suggests systematic overlooking of subtractive strategies, it turns out that many don’t and this bias can be modified by experimental conditions such as subtraction cues. Third, the effect of increased cognitive load can be demonstrated to increase the likelihood of additive rather than subtractive biases. Fourth, the biases extend across a number of domains including physical, social, and intellectual. Fifth, the authors suggest that there may be a number of “cognitive, cultural, and socioecological reasons for favoring the additive bias over the subtractive one.  Sixth, although the additive transformation was more likely to occur that does not mean it offers the best solution to the problem.  It may simply be the most commonly used solution. 

Real world experience illustrates how the additive transformations can be reinforced.  Advertising is a common one. The goal of advertising is basically to sell someone something that they don’t need or change their preferences for something that they do need to a different product.  If it works, it is an additive strategy on top of additive behavior.  If the product being sold affects other learning centers in the brain like reward-based learning that can lead to further additive effects. The photo at the top of this post illustrates another example.  This kitchen drawer for spoons and spatulas is a solution to the cooking problem of how many are needed to accomplish what the cook in this case needs to accomplish. The drawer is packed to the point where it barely closes and at that point, the cook is forced to reassess and decide about cleaning the drawer out and starting over.  Homeowners often forced to make similar downsizing or subtractive decisions after 20-30 years of additive ones and being forced with either space constraints or a smaller family.  

What about medical and psychiatric treatment?  I don’t think there is any doubt that additive transformations are operating. Most treatments that involve medication have a step approach with the addition of medications for symptoms that do not respond or partially respond to the initial treatment. This occurs after an explicit subtractive bias or at least a bias to maintain the status quo 20 years ago.  At that time, hospitals and clinics were reviewed based on criteria to limit the amount of polypharmacy defined as more than one drug from the same class. Today, polypharmacy is common.  Reference 3 below gives an example of polypharmacy defined as 5 or more medications taken concomitantly and hyper-polypharmacy was defined as 10 or more medications taken concomitantly in a 3-month sample of 404 geriatric patients with cardiovascular disease admitted to a hospital during 3-month period.  They found the prevalence of polypharmacy was 95%.  The prevalence of hyper-polypharmacy was 60%.  Most patients (77.5%) also had a potential drug-drug interaction.  Their suggestion be vigilant is a strategy discussed as being potentially successful in containing the additive strategies (2).  

From psychiatry, I am including a common problem that I encountered as a tertiary consultant.  That problem is what to do about a person with a depression that has not responded to high dose venlafaxine. There are geographic areas in the US, where very high dose venlafaxine is used with and without pharmacogenomic testing.  From the options listed in the diagram it is apparent that there are 4 additive (black arrows) strategies and 2 subtractive (red arrows). There is a robust literature on the additive strategies and not so much with the subtractive. As a result, it is common these days to encounter patients who have tried numerous combinations right up to and including “California Rocket Fuel” (4) of the combination of an SNRI like venlafaxine with mirtazapine.  The ways to analyze this situation, especially if there has not been any improvement are significant and depend a lot on patient preferences and side effects in addition to the lack of response. I have found that very high dose venlafaxine, can be sedating to a significant number of people and that they feel better when it is tapered.  I have also seen many people far along the augmentation strategies when tapering or discontinuing the venlafaxine was never considered. In some of these cases, the patient reports that venlafaxine is historically the only antidepressant that has worked for them in the past.

That brings up the issue of additive versus subtractive biases on the part of the patient. We have all been bombarded by pharmaceutical commercials suggesting the best way to mood stabilization is adding another medication – typically aripiprazole or brexpiprazole. In fact, those commercials speak directly to additive biases. It is often very difficult to convince a person to discontinue or reduce a medication that they have talked for years – even when careful review suggests it has been ineffective or creates significant side effects. 

Could a discussion of additive versus subtractive transformations be useful in those situations? There is currently no empirical guidance, but these might be additional experiments to consider for both prescribing physicians and the patients they are seeing. Certainly the expectations that they patient has for any given treatment needs to be discussed and whether that expectation is reasonable given their personal experience and the objective evidence. On the side of prescribing physicians, it is fairly easy to flag medication combinations that are problematic either from the perspectives of too many medications being used at once, physical and side effects not being analyzed closely enough, or medications being changed too frequently. Would discussing additive and subtractive strategies be useful in that setting?  Would a discussion of basic rules to address additive biases such as discontinuing a medication when it is replaced be useful?

Remaining vigilant that there are subtractive strategies out there is a useful lesson from this paper. Physicians are aware of the concept of parsimony and how that can be applied to medical care. Given the fact that the additive strategies are probabilistic and modifiable with conscious strategies – that should still prove to useful in containing polypharmacy.  

 

George Dawson, MD, DFAPA

Supplementary:

Another common additive strategy that I have encountered in the past 10 years is performance enhancement.  The patient presents not so much for treatment of a psychiatric problem but because they believe that adding a medication or two or three will improve their overall ability to function. Common examples would include:

1.  Presenting for treatment of ADHD (with a stimulant medication) not because of an attentional problem but because the stimulant creates increased energy and the feeling of enhanced productivity.

2.  Presenting for treatment of insomnia in the context of drinking excessive amounts of caffeine in the daytime and the caffeine is viewed as necessary to enhance energy at work or in the gym.  In some cases, stimulants are taken in the daytime and the idea is that the medication for insomnia would counter the effect of stimulants or caffeine taken late into the day.

3.  Taking anabolic androgenic steroids (AAS) and expecting to treat the side effects of mood disturbances, insomnia, anger, and irritability in order to keep taking the AAS.  Many AAS users also take other medications for this purpose as well as various vitamins, supplements, and stimulants to enhance work outs.

4.  Taking excessive numbers of supplements with no proven value and seeking to use medications for nondescript symptoms associated with the supplement use. In many cases, patients with psychiatric disorders are sold on elaborate mixtures of minerals and supplements with the promise that they address their symptoms.  In many cases it is difficult to determine if the associated vitamins and supplements interact with the indicated medical treatment or not.

All of these are additive strategies with no proven value that I have seen in the outpatient settings.  It is obviously important to know if the patient being treated is using these strategies.  There are often competing considerations – for example does the patient have a substance use disorder and are substance use disorders another predisposing condition to additive biases (I suspect they strongly are).

 

References:

1:  Meyvis T, Yoon H. Adding is favoured over subtracting in problem solving. Nature. 2021 Apr;592(7853):189-190. doi: 10.1038/d41586-021-00592-0. PMID: 33828311.

2:  Adams GS, Converse BA, Hales AH, Klotz LE. People systematically overlook subtractive changes. Nature. 2021 Apr;592(7853):258-261. doi: 10.1038/s41586-021-03380-y. Epub 2021 Apr 7. PMID: 33828317.

3:  Sheikh-Taha M, Asmar M. Polypharmacy and severe potential drug-drug interactions among older adults with cardiovascular disease in the United States. BMC Geriatr. 2021 Apr 7;21(1):233. doi: 10.1186/s12877-021-02183-0. PMID: 33827442; PMCID: PMC8028718.

4:  Stahl, SM . Essential psychopharmacology: neuroscientific basis and practical applications. Cambridge University Press, Cambridge 2000. p. 363.

 

Graphics Credit:

So far they are all mine.  Yes that is one of my kitchen drawers but I am fairly good at avoiding polypharmacy.  Click on any graphic to enlarge.