L14 Psychological Medicine Mental - physical comorbidity

Overview

This lecture defines mental-physical comorbidity as the co-occurrence of mental and physical disorders at greater than chance level, and distinguishes concurrent comorbidity (both conditions present around the same time) from lifetime comorbidity (one predisposing to the other much later in life). It works through the mechanisms in both directions, physical disease causing mental disorder and mental disorder causing physical disease, illustrated by a chronic pain case study, then presents evidence from the World Mental Health (WMH) Surveys linking prior mental disorders to the subsequent diagnosis of chronic physical conditions, before drawing out the clinical implications for both mental health and medical practice.

What is mental-physical comorbidity?

• Definition: co-occurrence of mental disorders and physical disorders at greater than chance level. Having a mental disorder increases the likelihood of developing a physical disease (relative to someone with no mental disorder history), and vice versa.
• Can manifest as:
  • Concurrent: both conditions evident at the same time, or the second arises soon after the first. This is the pattern most often seen clinically, e.g. a person with a recent heart attack who becomes highly anxious or depressed.
  • Lifetime: e.g. someone with recurrent depression in early to mid adulthood who develops heart disease later in life.
• US prevalence data (adults):
  • 25% have a mental disorder
  • 58% have a medical condition
  • 68% of adults with mental illness have at least one other medical condition
  • 29% of adults with a medical condition have a mental disorder

Physical disease to mental disorder: mechanisms

Three causal mechanisms by which a physical condition can lead to a mental disorder.

1. Psychological mechanisms: shock, anxiety, distress, especially if the condition is life threatening, or if it causes pain, disability, major lifestyle changes and restrictions, or changes to relationships.
   • Psychological effects of cancer specifically: fear of death and of recurrence (hypervigilance); a sense of hopelessness, loss of control, “betrayal”; stress of treatment and its side effects; stress of interactions with others (being avoided, being treated as if dying).
2. Medications prescribed for the physical condition:
   • Interferon (used for some cancers, hepatitis C) can cause depression.
   • Some anti-retrovirals for HIV can cause suicidality, mania, paranoia.
3. Biological mechanisms: the disease itself causes changes in the brain that then cause depression, e.g. vascular depression (inflammation and ischaemia) and Parkinsonian depression.

Case study: chronic pain and depression

A 42-year-old female artist with disabling chronic back pain, 5 years of largely unsuccessful treatment (medications, relaxation, physiotherapy), no significant prior mental disorder history, well functioning, good marriage, 2 children. Scheduled for surgery with high hopes for success. The surgery did not fix the problem: she became profoundly depressed and anxious, and suicidal. Her expectations were shattered, producing hopelessness and despair (“this will never get better”, “this was my last chance”, “I can never be happy again”). She was successfully treated with medication and CBT. This illustrates mechanism 1: a life-altering physical condition producing a mental disorder via psychological mechanisms, even with no prior psychiatric history.

Mental disorder to physical disease: mechanisms

• This pathway (mental to physical) is less intuitive and less well understood than the reverse.
• The time frame is often long term, because mental disorders usually start early in life while chronic physical disease tends to manifest later.
• The best-researched example: depression has repeatedly been found to be a factor associated with subsequent heart disease.

Three mechanisms:

• Via lifestyle behaviours: people with mental disorders are more likely to smoke, drink alcohol excessively, eat poorly, and get less exercise and sleep.
• Via biological pathways: stress response with HPA axis and SNS (sympathetic nervous system) axis hyperactivity; inflammation; mental disorders are viewed by some as “ageing accelerants”.
• Via medications: antipsychotics can cause obesity and metabolic syndrome.

World Mental Health Surveys: evidence for the mental-to-physical pathway

• Question addressed: whether a mental disorder experienced earlier in life is linked to the subsequent diagnosis of chronic physical conditions other than heart disease.
• The WHO World Mental Health (WMH) Surveys collected data on mental disorders (past and present) and diagnosis of chronic physical conditions across 30 countries and around 150,000 participants, allowing investigation of whether an earlier mental disorder was associated with a later diagnosis of a chronic physical condition.
• A specific published analysis (Scott et al., JAMA Psychiatry) drew on 18 face-to-face, cross-sectional household surveys of community-dwelling adults in 17 countries (47,609 individuals; 2,032,942 person-years), conducted from 1 January 2001 to 31 December 2011. The Composite International Diagnostic Interview was used to retrospectively assess lifetime prevalence and age of onset of DSM-IV mental disorders. It investigated associations of 16 temporally prior DSM-IV mental disorders with the subsequent onset or diagnosis of 10 chronic physical conditions.

The slide reproducing this paper is a screenshot of the printed journal page. The visible text ends partway through the Design/Setting/Participants paragraph, so the paper's Methods, Results and Conclusion are not available from the slides and are not summarised here.

Odds ratios by type of mental disorder

Adjusted for age, sex, country, smoking, education, child abuse. Asterisk (*) = statistically significant.

Chronic condition	Any mood disorder	Any anxiety disorder	Any impulse-control dx	Any substance-use dx	Any disorder
Arthritis	1.6*	1.5*	1.5*	1.5*	1.5*
Any chronic pain	1.6*	1.8*	2.0*	1.4*	1.8*
Heart disease	1.5*	1.7*	1.5*	1.6*	1.6*
Stroke	1.5*	1.5*	1.8*	2.1*	1.6*
High blood pressure	1.3*	1.4*	1.6*	1.6*	1.5*
Diabetes	1.3*	1.2*	1.9*	1.3*	1.2*
Asthma	1.5*	1.4*	1.4*	1.6*	1.5*
Chronic lung disease	2.0*	1.6*	2.3*	2.2*	1.9*
Peptic ulcer	1.6*	1.7*	1.7*	1.5*	1.8*
Cancer	1.2	1.2	1.5*	1.3*	1.2*

On this slide the Cancer row's "any mood disorder" (1.2) and "any anxiety disorder" (1.2) values are printed in red text rather than the black used elsewhere, and lack the significance asterisk carried by every other cell. The intended meaning of the red colouring (e.g. specifically non-significant) is not stated on the slide.

Odds ratios by number of mental disorders

Chronic condition	1 disorder	2 disorders	3 disorders	4 disorders	5+ disorders
Arthritis	1.4*	1.6*	1.9*	2.2*	2.5*
Any chronic pain	1.7*	2.0*	2.1*	2.0*	2.4*
Heart disease	1.5*	1.8*	2.2*	2.2*	2.5*
Stroke	1.2	2.1*	2.1*	2.6*	2.6*
High blood pressure	1.4*	1.6*	1.7*	1.6*	2.3*
Diabetes	1.1	1.2	1.6*	1.7*	2.3*
Asthma	1.3*	1.4*	1.8*	2.5*	2.2*
Chronic lung disease	1.7*	1.8*	3.5*	2.5*	3.4*
Peptic ulcer	1.5*	1.9*	2.3*	2.6*	2.5*
Cancer	1.2*	1.2	1.3	1.1	1.7*

The Cancer row is cut off at the bottom edge of the rendered slide image; its values above come from the slide's underlying text extraction rather than the image itself. Separately, the Stroke and Diabetes "1 disorder" cells (1.2 and 1.1) and the Diabetes "2 disorders" cell are printed in red text, matching the unexplained colour pattern flagged in the previous table.

Summary of WMH findings

• A wide range of mental disorders are associated with an increased likelihood (risk) of developing a wide range of physical conditions.
• The greater the number of mental disorders someone experiences, the greater the odds of subsequent physical disease.
• The earlier the onset of the mental disorder, the greater the likelihood of subsequent physical ill health.

Clinical implications

In mental health patients

• GPs and collaborating physicians need to assess lifestyle and physical disease biomarkers in mental health patients.
• This needs to start when the patient is still relatively young, because the pathogenesis of chronic physical conditions starts early in life, and bad health habits are harder to break the longer they continue.
• This is not happening routinely at present, and is only done to some extent for patients with psychotic disease.

"The scandal of premature mortality": mental health patients die 10 to 15 years earlier than those without mental disorders. This needs to change.

In medical patients

• Physicians whose primary focus is the physical disease need to be aware that conditions involving pain, disability, threat to life, or major lifestyle change can provoke psychological distress or mental disorders.
• People with a past history of mental health problems are the most vulnerable to this.
• Mental disorder comorbidity can greatly decrease treatment adherence, make treatment more complicated, and increase suffering.

Self-test

1. Define mental-physical comorbidity, and distinguish concurrent from lifetime comorbidity with an example of each.
2. In the US prevalence data given, what proportion of adults with a mental illness have at least one other medical condition, and what proportion of adults with a medical condition have a mental disorder?
3. Describe the three mechanisms by which a physical disease can lead to a mental disorder, giving an example of each.
4. In the chronic pain case study, what triggered the patient’s depression despite her having no prior mental disorder history, and how was she treated?
5. Why is the mental-to-physical causal pathway less well understood than the physical-to-mental pathway, and what is the best-researched example of it?
6. Describe the three mechanisms by which a mental disorder can lead to a physical condition, giving an example of each.
7. What question was the World Mental Health Surveys study trying to answer, and how was it designed (surveys, countries, timeframe, assessment tool)?
8. Summarise the three key findings of the WMH study relating the number and timing of mental disorders to subsequent physical disease risk.
9. List the clinical implications of mental-physical comorbidity for mental health patients.
10. Distinguish the clinical implications of mental-physical comorbidity in mental health patients from those in medical patients.
11. What is meant by “the scandal of premature mortality” in this context?
12. A patient with a past history of depression is diagnosed with heart disease. Based on the lecture, predict how this comorbidity might affect their treatment and why.

Answers

Reveal answers

1. Mental-physical comorbidity is the co-occurrence of mental and physical disorders at greater than chance level. Concurrent comorbidity is when both conditions are present at the same time or the second arises soon after the first, e.g. a person with a recent heart attack who becomes highly anxious or depressed. Lifetime comorbidity is when one condition arises long after the other, e.g. someone with recurrent depression in early to mid adulthood developing heart disease later in life.
2. 68% of adults with mental illness have at least one other medical condition; 29% of adults with a medical condition have a mental disorder.
3. (1) Psychological mechanisms: shock, anxiety and distress, especially when the condition is life threatening or causes pain, disability, lifestyle restriction or relationship change, e.g. the psychological effects of cancer (fear, hopelessness, treatment stress). (2) Medications prescribed for the physical condition, e.g. interferon causing depression, some HIV anti-retrovirals causing suicidality, mania or paranoia. (3) Biological mechanisms, where the disease causes brain changes that cause depression, e.g. vascular depression (inflammation and ischaemia) and Parkinsonian depression.
4. Her expectations were shattered when surgery for her chronic back pain failed to fix the problem, producing hopelessness, despair and suicidal depression and anxiety, illustrating the psychological mechanism (mechanism 1) even with no prior psychiatric history. She was successfully treated with medication and CBT.
5. It is less intuitive and less well understood because the time frame is often long term: mental disorders usually start early in life while chronic physical disease tends to manifest later, making the causal link harder to trace. The best-researched example is depression as a factor associated with subsequent heart disease.
6. (1) Via lifestyle behaviours: people with mental disorders are more likely to smoke, drink excessively, eat poorly, and get less exercise and sleep. (2) Via biological pathways: HPA and SNS axis hyperactivity (stress response), inflammation, and mental disorders acting as “ageing accelerants”. (3) Via medications: antipsychotics causing obesity and metabolic syndrome.
7. It aimed to find out whether mental disorders experienced earlier in life are associated with the subsequent diagnosis of chronic physical conditions (beyond heart disease). It drew on the WHO World Mental Health Surveys programme (30 countries, around 150,000 participants), with a specific published analysis using 18 cross-sectional household surveys in 17 countries (47,609 individuals) from 2001 to 2011, using the Composite International Diagnostic Interview to retrospectively assess lifetime mental disorders and their age of onset.
8. (1) A wide range of mental disorders are associated with increased risk of a wide range of physical conditions. (2) The greater the number of mental disorders experienced, the greater the odds of subsequent physical disease. (3) The earlier the onset of the mental disorder, the greater the likelihood of subsequent physical ill health.
9. GPs and collaborating physicians need to assess lifestyle and physical disease biomarkers in mental health patients, starting while the patient is still relatively young (since pathogenesis of chronic physical disease starts early and bad habits are harder to break over time). This is not happening routinely at present, except to some extent in patients with psychotic disease.
10. In mental health patients, the focus is on physicians proactively assessing lifestyle and physical disease risk from a young age, because this is not currently done routinely. In medical patients, the focus is on physicians recognising that the physical condition itself (pain, disability, threat to life, lifestyle change) can provoke psychological distress or mental disorder, particularly in those with a past mental health history, and that resulting comorbidity reduces treatment adherence, complicates treatment and increases suffering.
11. It refers to the fact that mental health patients die 10 to 15 years earlier than people without mental disorders, largely reflecting the unmanaged physical health burden described in the lecture.
12. Their past history of depression makes them more vulnerable to developing a mental disorder in response to the heart disease (via psychological mechanisms, especially if it is experienced as life threatening or life-altering). If comorbid mental disorder does develop, it can decrease treatment adherence, make managing the heart disease more complicated, and increase the patient’s suffering, so clinicians should proactively watch for and address psychological distress alongside the physical treatment.