Depression and psoriasis: Large study quantifies epidemiologic link

May 1, 2008

The first large-scale study to examine the epidemiologic link between depression and psoriasis shows that patients with psoriasis are significantly more likely to experience depression than patients with other diagnoses, dermatologic or otherwise, a study co-author says.

Key Points

"Be aware that there's a lot of depressive psychopathology among psoriasis patients," says Madhulika A. Gupta, M.D., professor of psychiatry at the University of Western Ontario, London, Ontario. "Smaller-scale studies have shown that when psoriasis patients are very depressed, they often do not adhere to treatment regimens, which in turn can complicate their response to standard dermatologic therapies," she says.

"This is why we decided to undertake this analysis," she says.

To circumvent the cost issue, Dr. Gupta and her co-authors - Aditya K. Gupta, M.D., Ph.D., professor, department of medicine, division of dermatology at the University of Toronto, and research associate and medical student Lauren Badalato, B.Sc. - relied on publicly available epidemiologic data. Specifically, they used reports of patient encounters between 1994 and 1996 from the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Care Survey (NHAMCS).

"The great thing about the NAMCS and other Centers for Disease Control and Prevention databases is that they include a nationally representative epidemiologic sample that allows researchers to generalize findings to the U.S. population as a whole," she says.

"These data are also free. Clearly, one has to format the data and run one's own analyses, but the data are available to anybody," Dr. Gupta says.

The fact that these data were collected routinely on all diagnoses, dermatologic and otherwise, makes them more robust than data gathered for specific studies with a particular a priori hypotheses behind them, she says.

"I find this data set to be very exciting, because these are real visits to outpatient and inpatient facilities," Dr. Gupta tells Dermatology Times.

Conversely, she says selection bias can occur when patients volunteer - and perhaps get paid - for specific studies.

"The clinician is not measuring NAMCS and NHAMCS data with a view of getting results that they're going to be writing up for publication," she says.

The NAMCS relies on a geographically diverse subset of office-based physicians to collect and report information about their patient encounters, with each physician reporting approximately 30 randomly chosen patient record forms during a specified one-week period.

The NHAMCS uses similar methods to capture data from hospital outpatient departments.

For each visit, physicians coded up to three diagnoses. For the study, researchers selected patients who received one or more dermatologic diagnoses (International Classification of Diseases/ICD codes 680 to 709) during the study period.

Researchers then divided this group of patients into those who were diagnosed with psoriasis, psoriatic arthritis and "other psoriasis."

Additionally, they considered demographic factors such as age, gender and race, while also creating an obesity variable in order to control for the possible confounding effects of this condition.

Ultimately, researchers found that among more than 150 million estimated dermatology visits to private offices and hospital outpatient clinics between 1994 and 1996, an estimated 4.7 million visits were for psoriasis. Of this group, approximately 57.4 percent of patients were female, 42.6 percent male and slightly more than half were over the age of 40.

Researchers also estimated the number of patients in whom physicians diagnosed depression at the time of the initial visit at nearly 91.5 million. When investigators controlled for obesity, alcoholism, age and gender, they found a significant association between depression and psoriasis (odds ratio/OR: 2.70, 95 percent confidence interval 1.57 to 4.62).

"I was surprised by how consistent these findings are with earlier reports. They really validate studies that have been done on smaller samples," Dr. Gupta says.

Furthermore, the study echoed previous findings regarding the relative impact of psoriasis on various age groups: the OR for depression and psoriasis was more than 4.5 in patients age 40 and under, versus approximately 1.8 for patients over age 40.

"A younger person with psoriasis tends to have more psychiatric comorbidity than an older person," she says.

When psoriasis occurs in a patient's late teens, 20s or 30s, Dr. Gupta says, "Because of the chronicity of the problem, the time that must often be taken away for treatments, and the cosmetic aspect of psoriasis and its effect on socialization, it affects the key tasks at that life stage - namely, socializing, finding a partner and establishing a career.

"Having to cope with psoriasis at a young age significantly interferes with those tasks."

She says it was also interesting to note that, consistent with other reports in the psychodermatologic literature, psoriasis was associated with significantly higher psychiatric comorbidity than other dermatologic conditions, regardless of patients' age.

Somewhat similarly, Dr. Gupta says an earlier study she and her colleagues published showed that the higher the degree of depression, the more itching patients reported (Gupta MA et al. Psychosom Med. 1994 Jan-Feb;56(1):36-40). Other studies have shown that high levels of pruritus are associated with a higher degree of suicidality, she says.

Therefore, Dr. Gupta says, "It's important for the clinician to be aware that a person who's more depressed may be having more dermatologic symptoms that are very distressing. They also could be suicidal."

To help identify these patients, she suggests asking not only whether patients have felt depressed, but whether they've lost interest in activities they normally enjoy.

"Often," she says, "a person will not acknowledge that they're depressed, so physicians must address the issue by addressing other features of clinical depression."

For physicians as well, Dr. Gupta says, "It's a question of awareness. If a patient is not getting better with standard treatments, perhaps there's underlying psychiatric morbidity that could be contributing to less-than-satisfactory response to dermatologic treatments."

Regarding study weaknesses, Dr. Gupta says that because data were collected by diagnostic code, "We do not have a severity variable. So we do not know how severe the psoriasis was for any particular patient."

Similarly, she notes that because confidentiality requirements made it impossible to track patient identities, multiple visits by the same patient possibly were all counted as separate visits.

"I have no way of knowing if that happened or not," Dr. Gupta says.

At press time, researchers were still analyzing their data. Their next step will involve year-by-year comparisons, in which Dr. Gupta says she expects the association between depression and psoriasis will hold true.