Other Causes of Dementia

Snapshot

• A 62-year-old man presents to his primary care physician due to trouble with walking and difficulty with concentrating. The patient describes his walking as if he is “stuck to the ground.” On gait testing, the patient has magnetic gait and on montreal cognitive assessment (MoCA) testing, he has a deficit in executive functioning. Laboratory tests are ordered and return normal. Lumbar puncture shows a normal opening pressure and magnetic resonance imaging (MRI) of the head is shown. (Normal pressure hydrocephalus)

Introduction

• Clinical definition
  • dementia describes a gradual and progressive decline in
    • memory and other cognitive abilities (e.g., language and visuospatial function)
• Etiology
  • dementia can be divided into
    • primary dementia
      • usually associated with neurodegenerative diseases (e.g., Alzheimer’s disease)
    • secondary dementia
      • due to secondary causes (e.g., hypothyroidism)
• Management
  • given the large array of causes of dementia
    • it is important to focus on identifying and treating reversible causes of dementia
  • laboratory tests such as
    • vitamin B12 levels
    • thyroid function tests
    • serum syphillis tests in endemic areas
  • MRI is ideally used
  • tests are ordered in order to support one’s clinical suspicion
• Examples of dementia given in section below

Vascular Dementia

• Clinical definition
  • a heterogenous syndrome leading to dementia secondary to
    • cerebrovascular disease that range from
      • mild deficits in cognition to frank dementia
• Epidemilogy
  • incidence
    • second most common cause of dementia after Alzheimer’s disease
  • risk factors
    • elderly
    • multiple vascular risk factors (e.g., atherosclerosis, lipohyalinosis, and cerebral amyloid angiopathy)
• Pathogenesis
  • cerebrovascular lesions impair brain function leading to
    • vascular dementia
• Presentation
  • clinial presentation is diverse and depends on where the damage is
    • cortical features
      • executive dysfuction and abulia/apathy in lesions affecting the
        • medial frontal lobe
      • aphasia in lesions affecting the
        • left parietal lobe
      • visuospatial difficulty in lesions affecting the
        • right parietal lobe
    • subcortical features
      • focal motor signs
      • unsteadiness and unprovoked falls
      • mild memory deficit
      • abnormal executive function
• Imaging
  • MRI may show
    • white matter lesions (leukoaraiosis)
      • this is a non-specific finding
    • cortical and/or sub-cortical infarcts
• Diagnosis
  • certain criteria highlights clinical findings suggestive of vascular dementia, such as
    • stepwise deterioration of cognitive function
      • memory impairment is of late-onset
    • hypertension
    • stroke history
    • focal neurologic symptoms
    • fluctuating symptoms
• Treatment
  • treat and prevent vascular risk factors
    • e.g., managing hypertension and diabetes
  • pharmacologic therapy
    • acetylcholinesterase inhibitors (e.g., donepezil)
• N-methyl-D-aspartate (NMDA) receptor antagonists (e.g., memantine)

Normal Pressure Hydrocephalus

• Clinical definition
  • pathologically enlarged ventricles in the setting of
    • a normal opening pressure noted on lumbar puncture
  • a potentially reversible cause of dementia
• Pathogenesis
  • believed to be due to
    • impaired cerebral spinal fluid (CSF) absorption which can be due to
      • previous intraventricular hemorrhage
      • previous subarachnoid hemorrhage
      • previous acute or chronic meningitis
      • Paget disease involving the
        • base of the skull
    • this results in fibrotic changes of the arachnoid granulations
• Presentation
  • the classic triad is
    • dementia
    • gait disturbances
    • urinary incontinence
• Diagnosis
  • MRI or CT of the head, which shows
    • ventriculomegaly that is not
      • completely attributable to cerebral atrophy
  • Lumbar puncture should show
    • normal (or mildly elevated) CSF opening pressures
• Treatment 
• ventricular shunting

Dementia Secondary to Infection

• HIV-associated neurocognitive disorder
  • clinical definition
    • cognitive impairement secondary to HIV infection and
      • cannot be explained by some other etiology
  • epidemiology
    • risk factors
      • lower CD4+ cell counts
  • presentation
    • in HIV-associated dementia
      • patients typically have a CD4+ cell count < 200 cells/μL
      • dementia
      • impaired executive function
      • subcortical dysfunction such as
        • impairments with attention and concentration
        • depressive symptoms
  • treatment
    • antiretroviral therapy (ART)
• Neurosyphilis 

Dementia Secondary to Metabolic Causes

• Thiamine deficiency (Wernicke-Korsakoff encephalopathy) 
• Vitamin B12 deficiency
• Hypothyroidism
• Alcohol-related dementia