The Diagnostic and Statistical Manual of Mental Disorders (DSM) is the official instruction book for diagnosing and treating mental health conditions in the US. It is used by psychiatrists, medical staff and academic researchers.

The DSM works based on the principle that psychological symptoms can be objectively classified and observed in the same way as physical symptoms, so psychiatric illness can be diagnosed and studied as medical illnesses. Emil Kraepelin, one of the first psychiatrists, pioneered this idea, which is why systems like the DSM are sometimes described as neo-Kraepelinian methods.

In Kraepelin’s time (1883), people were diagnosed haphazardly, based on their most obvious symptoms. Most doctors also believed in Unitary Psychosis, the idea that all symptoms of mental illness were variants of one overall illness. Kraepelin instead looked for syndromes – patterns and trajectories of symptoms. He wrote an encyclopaedia of psychiatry which contained case histories and trajectories of specific syndromes and also promoted his diagnostic system.

New disorders become part of a DSM in a complex process, which I’ll follow up on at some point. To over-simplify it slightly, you can split the process of noticing, labelling and classifying a disorder into three large steps. Each step should be based on lots of clinical research on patients, expert discussion, and psychological research.

But how does a patient get diagnosed with an existing disorder? The first step is to get information from the patient about how they feel and think, and whether they’ve noticed any changes in how they act and respond to situations. This information is then combined with the DSM guidelines, looking at the Diagnostic Classification, Diagnostic Criteria, and Descriptive Text for each disorder. An important note here is that even though the DSM aims be an objective description of recorded symptoms, reality is much messier. Because many criteria are about how a patient feels, and their subjective experiences, a patient’s diagnosis is often affected by how they explain their experiences to the psychiatrist, which can lead to people’s symptoms being overlooked or misinterpreted.

Other criteria are about symptoms observed by the psychiatrist. This can also cause conflict, because the psychiatrist must use their subjective judgement to make sense of what they hear from the patient and what they see in appointments. Unfortunately, this can lead to inconsistent or biased diagnoses – specific disorders can be diagnosed almost entirely in one gender just because the stereotype of that gender being more likely to have the disorder becomes self-fulfilling. Similarly. recent research on ADD and Autism Spectrum Conditions shows that women with either neurotype are often overlooked. This is because the original research identifying each neurotype was carried out on boys, and the symptoms found in boys were assumed to be universal. As a result, women and girls with either neurotype, who usually express slightly different symptoms than boys, were under-diagnosed and mis-diagnosed for decades.

Diagnostic Classification

This is the masterlist of everything currently classified as a disorder or illness by the American Psychological Association (the creators/publishers of the DSM). The APA also decides what disorders cannot be diagnosed together, and which external factors can affect how valid a diagnosis is.

To make a guess at a diagnosis, the psychiatrist will first see which DSM disorder most closely matches the patient’s displayed and volunteered symptoms. After that, the psychiatrist must then make sure the patient’s symptoms can’t be better explained by anything else. For example, if a patient complains of severe anxiety, the psychiatrist might find out that the patient drinks an unsafe amount of coffee; the overload of caffeine could be causing them anxiety, so this would need to be ruled out first.

What the APA considers a disorder can change over time. This is sometimes due to new information, such as research suggesting that one condition could be split into two narrower conditions so that diagnoses are useful. Sometimes, these changes are due to wider social changes. For example, until the DSM-III, being homosexual was considered a mental illness. In the DSM-IV, homosexuality itself wasn’t a disorder, but if someone was extremely distressed and disturbed by being homosexual, that distress could be classified as a disorder. This is a similar pattern to being transgender today: the DSM-IV discussed gender identity disorder, which would apply to anyone who doesn’t identify with the gender assigned at birth, then the DSM-5 replaced this diagnosis with gender dysphoria, which should only apply to people who experienced major distress and dysfunction about being transgender.

Once a list of disorders has been drawn up, the next part is to make it clear what sets of symptoms relate to each disorder, and what conditions support or prevent a diagnosis of each disorder.

Diagnostic Criteria Sets.

Criteria sets contain the list of symptoms for each disorder, and how many symptoms are usually required for a diagnosis. The DSM-IV criteria list for unipolar depression (otherwise known as Major depression) contains 9 items:a diagnosis requires someone to show at least 5 criteria, and they must show either the first or second criteria. (Some conditions have specific essential criteria, while other conditions are solely diagnosed by the number of symptoms). Severity is based on both how many individual symptoms are present, and their overall impact on the patients life.

Other criteria include:

• Time limits- a patient needs to have symptoms of Generalised Anxiety Disorder for six months before it can be officially diagnosed.
• Age limits for symptom appearance- ADD can be diagnosed at any age, but some symptoms have to have been noticeable before age 7. If all symptoms only appear in adulthood/ late adolescence, it cannot be diagnosed as ADD.
• Age limits for diagnosis, regardless of symptom appearance- Personality disorders cannot be officially diagnosed before age 18, as people’s personalities are seen as too malleable before then.
• Exclusion/ overriding criteria- if someone is diagnosed with unipolar depression, but then has a hypomanic episode, their diagnosis must change to bipolar depression instead.

Descriptive Text

Each disorder is accompanied by a more descriptive explanation of what a patient may look and sound like, how they might behave when talking to the psychiatrist, and what phrases people with the diagnosis commonly use to describe their experiences. For example, someone with unipolar depression might describe themselves as being in a “fog” or “black cloud”, while someone who has bipolar depression might view their depressive episodes as a “crash” or “hibernation” compared to their previous hypomania.

Descriptive text will also explain what tests could support or go against a diagnosis, and what treatment options are currently seen as most useful. Risk factors, genetic connections (if known) , and prognoses (how well people generally do after being diagnosed), are often included.

Cross-cultural factors and differences are required for some disorders, as people of different cultures (or different genders in the same culture) can explain the same disorder in different ways. For example, people living in Asian cultures are more likely to report unipolar depression and anxiety by their physical symptoms instead of emotional and personal symptoms, due to cultural differences in how mental health issues are perceived.

Finally, the disorders are organised into chapters based on their properties and connections; each version of the DSM will rearrange how disorders are grouped, due to more information on causes and treatments, or data on how the diagnoses have been used and how effective they have been.

Once they have been organised, disorders will then be given a 5-digit code; codes are designed to reflect connections between families of disorders, and variations within families, such as severity and length.

Diagnostic Codes.

A good way to make sense of DSM codes is to compare it to the Dewey Decimal System used in libraries. A library code, let’s say 513.21, can be translated into different degrees of information about the book. Putting 513.21 into the Dewey Decimal System gives us:

5 = Sciences and maths
51 = maths
513 = arithmetic
513.2 = arithmetic operations
513.21 = basics of arithmetic operations

For books, numbers before the decimal point narrow down the book to its field and subfield, while numbers after the decimal point are used to narrow down the difficulty level, authors, language and other useful information.

DSM codes look the same and often work similarly. Using Mood Disorders as my first example, Mood Disorders mostly occupy number 296 in the DSM.

Numbers after the decimal point are used to specify whether the person’s depression is new to them (Single Episode), or a pattern (Recurrent), as well as its current severity. The numbers are also used to indicate when a person is in remission from a condition (when their symptoms are reduced).

For example, the code 296.33 would break down into:

296 = a depressive disorder.
296.3 = major depressive disorder, recurrent type.
296.33 = severe, but without any elements of psychosis.

While 296. 45 would mean:

296 = a depressive disorder.
296.4 = bipolar depression type 1, where the person was most recently hypomanic rather than manic or depressed.
296.45 = in partial remission. (The person has lessened symptoms, usually meaning they are currently on medication).

If things aren’t quite as clear, there are also numbers put in place for that.

For Mood Disorders, 296.9 signifies Mood Disorder Not Otherwise Specified (NOS), aka “we know its some kind of mood disorder, but don’t yet know beyond that”, and 296.8 signifies Bipolar disorder NOS. However, Depression NOS is number 311, while Cyclothymia (which is thought to be a chronic but milder version of Bipolar depression) is at 301 alongside the Personality disorders.

Ok, maybe the DSM isn’t quite as organised as the Dewey Decimal system…