Neurological diseases, such as multiple sclerosis (MS), Parkinson’s disease (PD), Alzheimer’s disease/dementia (AD), and epilepsy, are known to carry a high risk of depression. Estimated prevalence rates of depression in each of these disorders vary greatly.1 For example, the lifetime risk for depression in patients with MS ranges from 40–60%.2 Estimates of the prevalence of depression in PD also vary widely, ranging from 7–76%.3 Depression in AD is estimated at 30–50%.4 Community-based studies of epilepsy populations report depression rates of 9–22%, and hospital-based samples report much higher rates (27–58%).5

Depression is frequently underdiagnosed and undertreated in patient with MS,6 PD,7 AD,8 and epilepsy.9 Reasons for this underdiagnosis might include the difficulty of distinguishing between depressive and neurological symptoms, and the communication limitations experienced by neurologically impaired patients, which make ordinary screening methods less effective.10

The wide variability of estimates of depression in individuals with neurological diseases can be attributed to inconsistencies in study design, inclusion criteria, and other influencing factors that differ from study to study.1 Additionally, many studies are based on comorbidities at a certain point in time rather than longtitudinally.1 To more accurately assess depression in MS, PD, AD, and epilepsy, Thielscher et al analyzed data from a major national German database, including data on of a total of 5,381,565 individuals. Of those, 42,914 patients who were newly diagnosed with these four conditions met the inclusion criteria of the study (ie, being treated by the same physician regularly prior to, during, and following the study; no history of depression or neurological disorder; and no cancer). The database collated drug prescriptions, diagnoses, and basic medical and demographic data directly obtained from the practice computer systems of general practitioners and specialists throughout Germany. The researchers analyzed information collected over a five-year period to assess how many patients with these neurological illnesses developed depression within that time period.

The researchers found that all four diseases increased the risk of developing depression at some point during the study period by a total of 8.3%, compared to the population at large. Of the patients with neurological disorders, those with MS showed the highest levels of depression (34.7%), followed by those with PD (33.4%), AD (31.5%), and epilepsy (22.4%). In all of these populations, prevalence of depression was higher in women than in men, and close to half of patients received were diagnosed with depression during the first year after diagnosis of their neurological disease. With AD, PD, and MS, patients under age 60 were more frequently diagnosed with depression during the five-year study period, while for those with epilepsy, this diagnosis was more frequent in those aged 60 or over.

The researchers commented, “The most striking result of our study is the high risk of developing depression as a consequence of . . . neurological diseases.” They noted that in AD and MS, it is unclear whether the increase in depression is pathophysiological or reactive in nature. In PD, it may be possible that depression is a side effect of drugs commonly used to treat the condition (L-dopa, amantadine, Baclofen, and bromocriptine). They added that patients with epilepsy experienced the lowest rates of depression, perhaps because some of the antiepileptic drugs (eg, carbamazepine, valproate, and lamotrigine) can support antidepressive treatment.

This is the first study that examines the longitudinal risk of developing depression in patients with neurological illnesses, using a consistent estimation method, and analyzing the differences between depressive risk gender, age, and each of the four conditions. The researchers conclude that MS, PD, AD, and epilepsy patients should be monitored routinely for depression, with particular emphasis given to the highest-risk groups (eg, females diagnosed with MS, younger patients confronted with dementia).

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