Depression and Anxiety
Anxiety and depression are significant risk factors for AD, and conversely, AD increases the likelihood of developing these psychiatric conditions. A systematic review of 14,760 studies showed dysthymia often emerges during the early stages of AD as an emotional response to cognitive decline.
Data from the Australian Imaging Biomarkers and Lifestyle study showed a markedly elevated risk for AD and MCI among individuals with preexisting anxiety or depression. This study also found that age, sex, and marital status are important determinants, with men and single individuals with depression being particularly susceptible to developing AD. Conversely, a cohort study of 129,410 AD patients with AD, 390,088 patients with all-cause dementia, and 3,900,880 age-matched controls without a history of depression showed a cumulative incidence of depression of 13% in the AD group vs 3% in the control group, suggesting a heightened risk for depression following an AD diagnosis.
These findings underscore the importance of targeted screening and assessment for patients with anxiety and depression who may be at risk for AD or those diagnosed with AD who are at risk for subsequent depression and anxiety. Although antidepressants are effective in treating depression in general, their efficacy in AD-related depression is of variable quality, probably owing to differing pathophysiologic mechanisms of the disease. Further research is necessary to explore both pharmacologic and nonpharmacologic interventions for treating depression in AD patients. Some studies have found that cognitive behavioral-therapy can be effective in improving depression in patients with AD.
Sleep Disorders
Research has shown a strong correlation between AD and sleep disorders, particularly obstructive sleep apnea, insomnia, and circadian rhythm disruptions. Additionally, studies suggest that insomnia and sleep deprivation contribute to increased amyloid beta production and tau pathology, hallmark features of AD. A scoping review of 70 studies proposed that this relationship is mediated by the glymphatic system (glial-dependent waste clearance pathway in the central nervous system), and that sleep deprivation disrupts its function, leading to protein accumulation and subsequent neurologic symptoms of AD. Another study showed that sleep deprivation triggers glial cell activation, initiating an inflammatory cascade that accelerates AD progression.
Given that the gold standard treatment for obstructive sleep apnea is continuous positive airway pressure (CPAP), it has been hypothesized that CPAP could also alleviate AD symptoms owing to shared pathophysiologic mechanisms of these conditions. A large systemic review found that CPAP use improved AD symptoms in patients with mild AD or MCI, though other sleep interventions, such as cognitive-behavioral therapy and melatonin supplementation, have yielded mixed outcomes. However, most studies in this area are small in scale, and there remains a paucity of research on treating sleep disorders in AD patients, indicating a need for further investigation.
Musculoskeletal Disorders
Although no direct causative link has been established, research indicates an association between osteoarthritis (OA) and dementia, likely because of similar pathophysiologic mechanisms, including systemic inflammation. Longitudinal analyses of data from the Alzheimer’s Disease Neuroimaging Initiative study found cognitively normal older individuals with OA experience more rapid declines in hippocampal volumes compared to those without OA, suggesting that OA may elevate the risk of cognitive impairment. Current treatments for OA, such as nonsteroidal anti-inflammatory drugs, glucocorticoids, and disease-modifying OA drugs, might also help alleviate AD symptoms related to inflammation, though the research in this area is limited.
AD has also been linked to osteoporosis. In a longitudinal follow-up study involving 78,994 patients with osteoporosis and 78,994 controls, AD developed in 5856 patients with osteoporosis compared with 3761 patients in the control group. These findings represent a 1.27-fold higher incidence of AD in patients with osteoporosis than in the control group, suggesting that osteoporosis might be a risk factor for AD.
Additionally, research has identified a relationship between AD and increased fracture risk and decreased bone mineral density, with AD patients exhibiting a significantly higher likelihood of bone fractures compared with those without AD. “Falls and fractures, aside from the risk they pose in all geriatric patients, in individuals with cognitive impairment — whether due to AD or another cause — have higher risk to cause delirium and that can result in greater morbidity and mortality and a lasting increase in cognitive disability,” stated Dr. Pascual-Leone. Current recommendations emphasize exercise and fall prevention strategies to reduce fracture risk in patients with AD, but there is a lack of comprehensive research on the safety and efficacy of osteoporosis medications in this population.
Implications for Clinical Practice
The intricate interplay between AD and its comorbidities highlights the need for a comprehensive and integrated approach to patient care. The overlapping pathophysiologic mechanisms suggest that these comorbidities can contribute to the evolution and progression of AD. Likewise, AD can exacerbate comorbid conditions. As such, a holistic assessment strategy that prioritizes early detection and management of comorbid conditions to mitigate their impact on AD progression would be beneficial. Dr. Pascual-Leone added, “The presence of any of these comorbidities suggests a need to screen for MCI earlier than might otherwise be indicated or as part of the treatment for the comorbid condition. In many cases, patients can make lifestyle modifications that improve not only the comorbid condition but also reduce its effect on dementia.” In doing so, healthcare providers can help improve patient outcomes and enhance the overall quality of life for individuals living with AD.
Alissa Hershberger, Professor of Nursing, University of Central Missouri, Lee’s Summit, Missouri, has disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.