Dementia

Key points

• Decline of memory + one of aphasia, apraxia, agnosia, executive function causing interference with daily function and independence
• Alzheimer's and Vascular dementia are commonest causes seen (> 70% combined)
• Each cause differs slightly in the chronology of symptoms and additional conditions
• Those resulting in Parkinsonism form a distinct sub-set
• Apart from dementia caused by Parkinson's disease the response to L-dopa is often limited
• The majority of dementias are irreversible but it is important to rule out and treat reversible causes

Alzheimer (60-80%)

• > 60 y.o
• Extracellular amyloid-beta protein (senile/neurtic plaquaes), intracellular neurofibrillary tangles, neuronal loss
• memory loss, visual-spatial skills (early), neuro-behavioural disorder (middle), v executive function, apraxia (later)
• may occur with Parkinsonism features

Vascular (10-20%)

• occurs after stroke
• abrupt onset, step wise deterioration (with further strokes)
• v executive function (early), v memory (late)
• CT/MRI = infarcts

Mixed dementia

• Combined features of above

Fronto-temporal dementia

• Younger age range of onset
• Several clinical subtypes with variations (see below)

Clinical subtypes

• Frontal - abnormal personality and social function, unusual eating habits, ritualised behaviours, cognitive problems (late)
• Aphasic - expressive dysphasia
• Temporal - receptive dysphasia (naming object, understanding words, face recognition)
  +/- motor neurone disease (weakness), progressive supranuclear palsy (loss downard gaze), corticobasal degneration (apraxia, agnosia)
  brain specimens may show tau or ubiquitin inclusions

Dementias with Parkinsonism

Dementia with Lewy bodies

• Second most common neuro-degenerative cause (not second cause)
• Cortical +/- subcortical Lewy bodies (round, eosinophilic, nucleic inclusions)
• Fluctuating cognition, visual hallucinations, Parkinsonism
  +/- falls, syncope, delusions, non-visual hallucinations, sleep disorders, depression

Progressive supranuclear (PSP) Dementia

• globose neurofibrillary tangles, sub-cortical tau proteins
• symmetrical Parkinsonism, downward gaze abnormality, pseudobulbar palsy (dysarthria, dysphagia) +/- apathy, disinhibition, dysphoria, anxiety

Cortico basal degeneration

• Asymmetric Parkinsonism +/- ideomotor apraxia (unable to copy movements), limb agnosia, aphasia,

Multi-system atrophy (includes Shy-Drager syndrome)

• Alpha-synuclien glial inclusions
• Symmetrical Parkinsonism but no tremor +/- dysautonomia, cerebellar signs, pyramidal signs

Reversible dementias

• Medication related - CNS depressants, psychotropics
• Alcohol intoxication/withdrawal
• Metabolic - electrolyte abnormalities, renal or hepatic failure
• Nutritional - B12
• Endocrine - thyroid
• CNS lesions - tumours, bleed, infection, Normal pressure hydrocephalus (gait disturbance, incontinence)

The 'Dementia Screen'

• FBC - ^ WCC (infection), macrocytosis (B12/folate deficiency)
• EUC - v^ sodium v^ calcium, renal failure
• LFTS - hepatic failure
• CXR - chest infection, lung tumour
• B12/folate
• Thyroid function tests - hypo/hyperthyroidism
• Blood culture - septicaemia
• Urine culture - urinary tract infection
• Syphilis serology - Generaly paralysis of the insane
• HIV serology - HIV encephalopathy
• CT brain - tumours, bleeding, hydrocephalus, abscess
  

Depression ('pseudodementia') may mimic the cognitive deficits of dementia