May 2019 By

Introduction to Dementia

Dementia is a progressive neurocognitive decline of sufficient magnitude to interfere with normal social or occupational functions, or with usual daily activities. It is a broad diagnostic category that includes Alzheimer's disease, Lewy Body dementia (15%), Frontotemporal dementia, Vascular dementia, Parkinson's disease, and Creutzfeldt–Jakob disease.

When being asked to see a patient with demenita, it is good to have a systematic approach. The following is one approach to diagnosing dementia.[1]

  1. Rule out delirium. Is there an acute onset and fluctuating course + inattention + disorganized thinking? Is there altered level of consciousness?
    • Urinary Tract Infections (UTIs) are especially common in the elderly and frequent culprits of delirium! Don't forget that a negative urine culture does not always mean there is no UTI, especially if the patient is symptomatic.[2]
  2. Rule out depression (“pseudodementia”). Consider atypical presentations: anxiety, irritability, unexplained physical complaints, worsening cognition. Once the depression is treated, the dementia symptoms go away!
  3. Rule out any substance use disorders
  4. Rule out any reversible causes
    • Order CBC (anemia), TSH (hypothyroidism), creatinine, electrolytes (hyponatremia), calcium (hypercalcemia), glucose (hyperglycemia), and vitamin B12 (vitamin B12 deficiency)
    • Creatinine (to assess renal function and ability to clear medications)
    • Consider neuroimaging such as CT or MRI
    • Consider rapid plasma reagin (RPR), LFTs
  5. Is it dementia, mild cognitive impairment (MCI), or normal aging?
    • Dementia: objective findings of cognitive loss with impairment of ADLs
    • MCI: objective findings of cognitive loss without impairment of ADLs Normal cognitive aging: no objective findings of cognitive loss

Common Dementia Subtypes and Presentation

Subtype Prevalence Typical presentation
Alzheimer's Disease (AD) ~50% Initial short-term memory loss
Vascular Dementia* ~25 % Vascular risk factors; neuroimaging evidence of cerebrovascular involvement
Lewy Body Dementia (LBD) 15% Bradykinesia or features of parkinsonism, fluctuating cognition, visual hallucinations
Frontotemporal Dementia (FTD) 3% Younger age, behavioural symptoms, or language impairment
Parkinsons's Disease Dementia (PDD) Most cases of PD will progress to dementia Dementia occurring > 1 year after onset of Parkinson disease motor symptoms

Dementia is not often due to one pathology. Some studies have shown that in a general population, 40% of patients have a combination of Alzheimer's Disease (AD) and vascular dementia, while only 30% had pure Alzheimer's and 12% had pure vascular dementia (VaD). About 12% had Alzheimer's combined with Parkinsons's Disease Dementia (PDD) (PD) or Lewy Body Dementia (LBD).[3]