Lewy body dementia (LBD)

Lewy body dementia is an increasingly recognised cause of dementia, accounting for up to 20% of cases. The characteristic pathological feature is alpha-synuclein cytoplasmic inclusions (Lewy bodies) in the substantia nigra, paralimbic and neocortical areas.

The relationship between Parkinson's disease and Lewy body dementia is complicated, particularly as dementia is often seen in Parkinson's disease. Also, up to 40% of patients with Alzheimer's have Lewy bodies.

Features

• progressive cognitive impairment
  • typically occurs before parkinsonism, but usually both features occur within a year of each other. This is in contrast to Parkinson's disease, where the motor symptoms typically present at least one year before cognitive symptoms
  • cognition may be fluctuating, in contrast to other forms of dementia
  • in contrast to Alzheimer's, early impairments in attention and executive function rather than just memory loss
• parkinsonism
• visual hallucinations (other features such as delusions and non-visual hallucinations may also be seen)

Diagnosis

• usually clinical
• single-photon emission computed tomography (SPECT) is increasingly used
  • it is currently commercially known as a DaTscan. Dopaminergic iodine-123-radiolabelled 2-carbomethoxy-3-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (123-I FP-CIT) is used as the radioisotope
  • the sensitivity of SPECT in diagnosing Lewy body dementia is around 90% with a specificity of 100%

Management

• acetylcholinesterase inhibitors

+rivastigmine is preferred because it has the best evidence for improving both cognitive and neuropsychiatric symptoms, particularly visual hallucinations and fluctuations in attention, while being relatively well tolerated

• tends to cause less worsening of parkinsonism than other cholinesterase inhibitors, likely due to its dual inhibition of both acetylcholinesterase and butyrylcholinesterase.
• neuroleptics should be avoided in Lewy body dementia as patients are extremely sensitive and may develop irreversible parkinsonism. Questions may give a history of a patient who has deteriorated following the introduction of an antipsychotic agent