Comorbidity in Mental Health and Medicine

By Gene Tang

Photo by Joshua Fuller on Unsplash

Comorbidity is a major challenge that has emerged in the fields of psychology, psychiatry, and medicine within the last few decades. While many people may not have heard this term

before, the concept behind it may be quite familiar. Comorbidity is associated with adverse outcomes at various scopes, from personal to clinical health care level. To this end, comorbidity is an issue that needs to be addressed.

Comorbidity as a term was first introduced by A. R. Feinstein, a well-known American doctor and epidemiologist. The term referred to the co-occurrence of multiple mental or physical health conditions within individuals. The term 'comorbidity' became somewhat fashionable not only in the field of psychiatry but also in general medicine [1], as its uses became increasingly frequent across different fields.

The prevalence of comorbid disorders is not limited to the co-occurrence of multiple mental disorders or multiple physical disorders, but simultaneous mental and physical disorders are also possible. Comorbid diseases and disorders have undoubtedly increased over the past few decades and it is likely that this trend will continue in the following years. This issue applies across many demographics; people of all ages can still suffer from numerous conditions, whether they are young or elderly. Norman Sartorious, a former president of the World Psychiatric Association, saw comorbidity as more of a rule than an exception [2] as it is now more prevalent than ever before. Thus, it is not at all uncommon for individuals to be diagnosed with comorbid illnesses.

So what causes comorbidity? Several factors may be contributing to its increasing prevalence. It is undoubtedly tricky, potentially even impossible, to pinpoint a singular root of the problem. However, one of the possible causes might be linked to people’s lifestyles in our contemporary world. An epidemic of unhealthy lifestyles, including changes in consumption and increased exposure to detrimental environments, may offer us an explanation for this phenomenon. These lifestyle changes can lead to an increased intake of pollutants and mutagens, which in turn, can play a part in one's immunological susceptibility against comorbid diseases and disorders. Another reason may be the success and advances in the field of medicine. Being able to prolong and sustain life without completely curing one disease could make it easier for patients to contract multiple illnesses simultaneously [2].

Even though external factors mentioned previously could partly inform the observed prevalence of comorbidity, the use of psychiatric classifications may explain another part of this story, particularly when it comes to mental health comorbidity. DSM (Diagnostic and Statistical Manual of Mental Disorders) plays a central role in the theoretical debate on comorbidity [3]. The proliferation of having such diagnostic categories was amongst other arguments made to inform the emergence of psychiatric comorbidity [1]. The argument asserts that the increase in the number of diagnostic categories may result in a higher likelihood of individuals being diagnosed with an illness and, consequently, increased comorbidity rates.

Another argument points to the problem of diagnostic inflation. Due to frequent revisions of diagnostic criteria [5], new diagnoses and lowered, easy-to-meet thresholds were introduced, thus significantly increasing the comorbidity rates [4]. The diagnostic criteria for anorexia nervosa can well exemplify this issue. In DSM-V, the number of necessary symptoms required for any patient to be diagnosed with anorexia nervosa was reduced from four to three [6]. This can be problematic because patients will not only have an increased likelihood of being diagnosed with anorexia nervosa but also potentially higher comorbidity rates. With this in mind, we could probably agree that it is not unlikely for an individual to be diagnosed with additional disorders once diagnosed with one.

Studies from different countries have found a similar statistical trend regarding this issue. In the US, it was found that 54% of those who met the criteria for at least one mental health disorder at some stage in their lives, also met the criteria for two or more other disorders. Meanwhile in Australia, 40% of those who met criteria for at least one disorder in the period of 12 months also met the criteria for two or more disorders [7]. For New Zealand, the number falls to around 37%, meaning that over a third of people with any disorders will also have more than one disorder [7].

Now let us look at a smaller scale, focusing on the patterns of comorbidity on specific mental disorders. In NZ, of the people diagnosed with anxiety disorders, approximately 27% also suffered from a comorbid mood disorder, and 9% had a comorbid substance use disorder. We can see that comorbidity occurs quite often in anxiety disorders. In fact, social anxiety disorder (SAD, which is a major type of anxiety disorder), was reported to have a considerably high comorbidity prevalence rate across different populations. This rate could sit as high as 90% [8]. The high rate of comorbidity we see in SAD may partly be due to how this disorder was found to be a predictor for the development of other disorders [9,10]. SAD subsequent disorders like mood disorders (e.g., depression, bipolar disorder, and dysthymia), therefore commonly co-occur with anxiety disorders [8]. This overlap was also the most common comorbidity in the NZ population, as reported in Te Rau Hinengaro.

Even though numerous studies on mental health comorbidity pay attention to anxiety disorders, we cannot disregard the fact that comorbidity can occur with any disorders of any form. That is, comorbidity does not necessarily have to come in the form of mental-mental comorbidity, but it can also be a mental-physical or physical-physical one.

Now that we know the potential causes of comorbidity and its prevalence in the population, we might ask ourselves, why is this a problem? Why is this important? Comorbidity is associated with a variety of adverse outcomes. First of all, overlapping symptoms or co-existing disorders may make prognoses extremely difficult. The presence of multiple disorders may create serious complications that limit clinicians from producing accurate diagnoses, and increase the rate of misdiagnoses. Secondly, comorbidity is associated with worse health outcomes. People who have comorbid diseases are more likely to have increased severity of the disease. More than 59% of the patients in NZ who suffered three or more disorders were classified as serious or severe cases [7]. This will undoubtedly impact the mortality as well as the general quality of life of the patients. Another significant issue that emerged from comorbidity and has been highlighted in several papers is the treatment difficulty [2,5,8]. The nature of co-existing diseases might result in inadequate and inappropriate treatment responses. When multiple diseases are comorbid, overlapping medication could be one of the problems. Some medications may restrict the effects of other medication required for the additional disorders suffered by the patient. That is, the potential interactions between medications can induce unwanted side effects. For example, a drug prescribed for chronic obstructive pulmonary disease will have an antagonistic effect on the diabetes treatment [11]. This shows that the medication or treatments prescribed in comorbid disease have the potential to be inefficacious.

Photograph by Robina Weermeijer on Unsplash (June 2019)

Another major concern raised when it comes to diagnosing comorbidity is that sometimes clinicians fail to recognize or overlook the comorbidity that exists [2,8]. A psychiatrist we previously mentioned, Norman Sartorious, had made some noteworthy arguments regarding this. He argued that clinicians are usually focusing on the disorders or diseases they are already familiar with. This seems to be commonly the case for mental-physical comorbidity. Non-psychiatric specialists tend to avoid making the diagnosis of mental health disorders due to the unfamiliarity and uncertainty about the treatments and diagnosis. Clinicians often would proceed with a single-disease treatment, expecting psychological symptoms to fade after treating the physical disease [2]. This is also the case for psychiatrists. Because they are unfamiliar with physical diseases, they might avoid conducting the examinations necessary to detect the presence of another concomitant disease.

At the end of the day, we all know that comorbidity is something that will continue to persist and we cannot expect the rate to drop anytime soon. However, what can be done or changed is the way professionals deal with this issue. Health care should not just focus on treating one specific disease, but rather should treat the patient holistically [12]. Hence, clinicians need to be trained and become competent in treating comorbid conditions. They need to understand their responsibility in dealing with various diseases and the diagnoses, even if some conditions are not their area of expertise. Non-psychiatric specialists should be able to confidently identify psychiatric disorders and likewise, psychiatrists should also be able to deal with physical illnesses competently. Having said that, we still need to understand that this may not be entirely possible—not without the reorientation of medical education. Therefore, clinicians may want to consider involving other specialists in the patients' diagnostic and treatment strategies. This will offer patients more accurate diagnoses as well as an assurance that comorbid diseases are not left undetected. To this end, we could say that the coordination and cooperation of professionals are essential in dealing with comorbidity.

Comorbidity is a big challenge that people are often unaware of. Even if we may not have heard about it before, it does not mean that it is not present in the world around us. We cannot forget that there are people out there whose lives have been devastatingly affected by this problem. The seriousness of this issue should not be underestimated, regardless of whether we are health professionals or not.

References

[1] Maj, Mario. “‘Psychiatric comorbidity’: an artefact of current diagnostic systems?,” British Journal of Psychiatry 186. no. 3 (Jan 2005): 182-184.

[2] Sartorious, Norman. “Comorbidity of mental and physical diseases: a main challenge for medicine of the 21st century,” Shanghai Archives of Psychiatry 25. no. 2 (Apr 2013): 68-69.

[3] Van Loo, Hanna M., and Jan-Willem Romeijn. “Psychiatric comorbidity: fact or artifact?,” Theoretical Medicine and Bioethics 36. no. 1 (Feb 2015): 41-60.

[4] Vella, G, M. Aragona, and D. Alliani. “The complexity of psychiatric comorbidity: a conceptual and methodological discussion,” Psychopathology 33. no. 1 (Feb 2000): 25-30.

[5] Batstra, Laura, and Frances Allen. “Diagnostic Inflation : Causes and a Suggested Cure,” Journal of Nervous and Mental Disease 200. no. 6 (June 2012): 474-479.

[6] American Psychiatric Association. Diagnostic and statistical manual of mental disorders: DSM-5. Arlington: American Psychiatric Association, 2013.

[7] Scott, Kate M. Te Rau Hinengaro: The New Zealand Mental Health Survey. Chapter 5: Comorbidity. Wellington: Ministry of Health, 2006.

[8] Koyuncu, Ahmet, Ezgi İnce, Erhan Ertekin, and Raşit Tükel. “Comorbidity in social anxiety disorder: diagnostic and therapeutic challenges,” Drugs in Context 8, (2019): 21573.

[9] Ohayon, Maurice M., and Alan F. Schatzberg. “Social phobia and depression: Prevalence and comorbidity,” Journal of psychosomatic research 68. no. 3 (2010): 235-243.

[10] Kessler, R. C., P. Stang, H.-U. Wittchen, M. Stein and E. E. Walters. “Lifetime co-morbidities between social phobia and mood disorders in the US National Comorbidity Survey,” Psychological Medicine 29. no. 3 (May 1999): 555-567.

[11] Valderas, Jose M., Barbara Starfield, Bonnie Sibbald, Chris Salisbury, and Martin Roland. “Defining Comorbidity: Implications for Understanding Health and Health Services,” Annals of Family Medicine 7. no. 4 (July 2009): 357-363.

[12] Gijsen, Ronald, Nancy Hoeymans, Francois G. Schellevis, Dirk Ruwaard, William A. Satariano, and Geertrudis A. M. van den Bos. “Causes and consequences of comorbidity: A review,” Journal of clinical epidemiology 54. no. 7 (July 2001): 661-674.