Neurocognitive Disorders: Pain Expression in the Face of Mental Deficits

There are an estimated 35 million people with dementia worldwide.¹ This figure is expected to increase to 100 million by the year 2050.² More compelling for pain practitioners is that the rate of dementia is known to rise with age to over 50% in those 90 years of age or older,³ and the prevalence of chronic pain is 72% in those 85 years or older.⁴

The most common cause of dementia is Alzheimer’s disease, but dementia due to vascular, frontotemporal, and Lewy bodies are also prevalent.¹ In all subtypes of dementia, specific neuropathological changes are responsible for the decline in function, cognition, and other symptoms, such as behavioral disturbances, psychological problems, and the breakdown of language and communication. Those with pain and dementia often express their pain through behavioral disturbances, such as agitation, screaming, and aggression.¹

In the current Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), the chapter on neurocognitive disorders (NCD) begins with delirium, followed by the syndromes of major NCD (previously dementia), mild NCD, and their etiological subtypes due to Alzheimer’s disease; vascular, Lewy bodies, Parkinson’s disease, frontotemporal, traumatic brain injury, HIV infection, substance/medication-induced, Huntington’s disease, prion disease, multiple etiologies, and other medical conditions.⁵ The primary clinical deficit that these disorders have in common includes cognitive dysfunction that is acquired rather than developmental.⁵

Setting the Stage for Neurocognitive Pain Management

The prevalence of delirium in the community is low (1–2%) but increases with age, rising to 14% among individuals older than 85 years.⁶ Overall prevalence estimates for major NCD are approximately 1–2% at age 65 years and as high as 30% by age 85 years.⁷ Estimates of the prevalence of mild NCD among older individuals are fairly variable, ranging from 2-10% at age 65 and 5-25% by age 85.⁸

The prevalence of mild NCD based on their etiological subtypes are as follows:

• Alzheimer’s disease ranges from about 60-90%, depending on the setting and diagnostic criteria⁹
• Vascular-related conditions range from 0.2% in the 65–70 years age group to 16% in individuals 80 years and older¹⁰
• Lewy bodies range from 0.1-5% of the general elderly population, and from 1.7-30.5% of all dementia cases¹¹
• Parkinson’s disease steadily increases with age from approximately 0.5% between ages 65 and 69 to 3% at age 85 years and older¹²
• Conditions originating in the frontotemporal region are in the range of 2–10 per 100,000¹³
• Traumatic brain injury-associated disability is about 2% of the general population¹⁴
• HIV infection affects approximately one-third to over one-half of individuals depending on the stage of the disease¹⁵
• Substance/medication-induced disorders are more likely to arise in those who are older and have a history of longer drug use, and/or have other risk factors such as nutritional deficits¹⁶
• Huntington’s disease in North America, Europe, and Australia is 5.7 per 100,000¹⁷
• The prevalence of prion disease is unknown

Keep in mind that several of the NCDs frequently coexist in patients with dementia.

Attending to the Comorbidity of Pain and Dementia

Scientific interest in the comorbidity of pain in NCD is relatively new. The literature indicates that the prevalence rate of patients with dementia that are regularly in pain varies from around 20% to higher than 50%.¹⁸ Evidence reflects that around 60-80% of individuals with NCD in dependent-care (nursing home) settings regularly experience pain, usually related to musculoskeletal, gastrointestinal, cardiac conditions, genitourinary infections, pressure ulcers in the skin, and/or orofacial pain.^19-20

There have been few studies on pain in different subtypes of NCD, such as dementia due to vascular, frontotemporal, and Lewy bodies. Approximately 35% of stroke patients suffer from post-stroke central neuropathic pain, which also occurs in vascular dementia.²¹ The prevalence of some type of pain (musculoskeletal, dystonic, radicular-neuropathic, and central neuropathic pain) in Parkinson’s disease ranges from 68-85%.²² In terms of traumatic brain injury-associated disabilities, the prevalence of chronic pain is about 52% among civilians²³ and at least 42% among veterans with comorbid post-traumatic stress disorder (PTSD) and persistent post-concussive symptoms.²⁴

How do neuropathological changes in NCD effect pain?

Current theory states that the areas of the brain involved in pain processing can be divided into two networks, the medial and lateral pain systems. The medial pain system is the pathway that mediates cognitive-evaluative and motivational-affective aspects of pain and is comprised of the amygdala, medial thalamus, hippocampus, anterior cortex cinguli, and prefrontal cortex. The lateral pain system is a pathway that mediates the sensory-discriminative aspects (localization, intensity, and quality of pain), which is comprised of the primary somatosensory areas and the lateral thalamic nuclei.²⁵ There may be an overlap between the two systems in the insula (the region of the brain that separates the frontal and parietal lobes from the temporal lobe).