How Much Overlap Exists Between Mental Health Diagnoses in the DSM-5?

What you need to know

• The researchers identified 628 distinct symptoms across 202 mental health diagnoses in the DSM-5
• About 37% of these symptoms appear in multiple diagnoses, sometimes across very different disorders
• Symptoms of major depressive disorder are especially common across many different diagnoses
• This symptom overlap may contribute to high rates of comorbidity (having multiple diagnoses) and diagnostic confusion

Understanding mental health diagnoses and symptom overlap

When you visit a mental health professional, they may use a manual called the Diagnostic and Statistical Manual of Mental Disorders (DSM) to help determine if you meet criteria for a specific mental health diagnosis. The DSM lists symptoms for each disorder, and clinicians check if you have enough of those symptoms to qualify for a diagnosis.

However, this new study reveals that many symptoms listed in the DSM appear in the criteria for multiple different disorders. This overlap in symptoms across diagnoses raises some important questions about how we classify and understand mental health conditions.

How the researchers examined symptom overlap

The researchers carefully went through the diagnostic criteria for 202 mental health disorders in the DSM-5 (the most recent version). They identified all the individual symptoms listed and looked for any that were repeated across different diagnoses.

This was a huge undertaking - they had to examine over 1,400 symptoms across all the different disorders! To help with this massive task, they used both human reviewers and computer programs that can analyze language.

Key findings on symptom overlap

After their detailed analysis, here’s what the researchers found:

• There are 628 distinct symptoms listed across all the DSM-5 diagnoses they examined
• 397 of these symptoms (about 63%) are unique to just one disorder
• 231 symptoms (about 37%) appear in the criteria for multiple disorders
• These overlapping symptoms show up a total of 1,022 times across different diagnoses
• Some symptoms appear in as many as 22 different disorders!

So while most individual symptoms are specific to one disorder, the symptoms that do overlap account for over 70% of all symptom listings in the diagnostic criteria. This means there’s actually quite a bit of repetition across different mental health diagnoses.

Which symptoms overlap the most?

The researchers identified the symptoms that appear most frequently across different diagnoses. The top 5 most common overlapping symptoms are:

1. Insomnia (difficulty sleeping) - appears in 22 different diagnoses
2. Difficulty concentrating - appears in 17 diagnoses
3. Hypersomnia (excessive sleepiness) - appears in 17 diagnoses
4. Irritable mood - appears in 16 diagnoses
5. Psychomotor agitation (restlessness) - appears in 16 diagnoses

Interestingly, many of the most common overlapping symptoms are typically associated with depression. In fact, 10 out of the top 15 most frequently appearing symptoms are part of the diagnostic criteria for major depressive disorder.

Differences between types of mental health disorders

The researchers also looked at how much symptom overlap occurred within and between different categories of mental health disorders. Some interesting patterns emerged:

• Some categories, like elimination disorders (e.g. bedwetting), gender dysphoria, and paraphilic disorders, had no symptom overlap with other categories at all
• Other categories, like bipolar disorders, trauma-related disorders, and personality disorders, had extensive symptom overlap both within the category and with other types of disorders
• Anxiety disorders had a lot of symptom overlap with other categories, but very little overlap between different anxiety disorders

Why does this symptom overlap matter?

The extensive overlap in symptoms between different mental health diagnoses has some important implications:

Diagnostic accuracy

When many symptoms appear across multiple disorders, it can make it harder for clinicians to accurately distinguish between different diagnoses. For example, sleep problems and difficulty concentrating could potentially point to depression, anxiety, trauma, or several other conditions.

Comorbidity rates

Comorbidity refers to when someone meets criteria for multiple mental health diagnoses at the same time. The symptom overlap identified in this study may help explain why comorbidity rates are so high - if many of the same symptoms appear in different diagnostic criteria, it becomes easier to meet the threshold for multiple diagnoses simultaneously.

Understanding causes and mechanisms

When studying the causes and underlying mechanisms of mental health conditions, focusing on diagnoses with extensively overlapping symptoms may obscure important distinctions. For example, studying “depression” as a single construct may miss key differences between various depressive symptoms that appear across many disorders.

Treatment approaches

Many evidence-based psychological treatments are designed to target specific diagnoses. But if those diagnoses actually share many symptoms with other conditions, it raises questions about how specific these treatments really are and whether more transdiagnostic approaches (targeting shared symptoms or processes) might be beneficial.

Rethinking mental health classification

The findings of this study add to a growing body of research questioning traditional diagnostic categories in mental health. Some researchers argue that we need new approaches that better capture the complexity of how mental health symptoms manifest.

Some alternative ideas that have been proposed include:

• Focusing more on individual symptoms rather than broad diagnostic categories
• Identifying clusters of symptoms that frequently occur together, even if they cross traditional diagnostic boundaries
• Examining underlying psychological, social, and biological processes that may contribute to multiple types of mental health problems

Conclusions

• There is substantial overlap in the symptoms used to diagnose different mental health disorders in the DSM-5
• This overlap is especially pronounced for symptoms associated with depression
• Symptom overlap may contribute to diagnostic confusion and high comorbidity rates
• These findings support the need to rethink how we classify and understand mental health conditions
• Future research should examine how this symptom overlap impacts diagnosis, treatment, and our understanding of the causes of mental health problems

While diagnostic manuals like the DSM serve an important purpose, this research highlights some of their limitations. As our understanding of mental health continues to evolve, new and more nuanced approaches to classification may emerge that better capture the complex reality of psychological distress and disorder.