Lewy bodies are abnormal microscopic deposits of protein that develop inside nerve cells, and cause a progressive dementia.
Outside the brain stem, Lewy bodies are associated with more profound cholinergic loss than in Alzheimer’s disease.
In the brain stem, Lewy bodies are associated with dopaminergic loss and symptoms similar to Parkinson’s disease.
People with cognitive symptoms and parkinsonian features developing within 1 year are, by convention, classed as having dementia with Lewy bodies. People with Parkinson’s disease who develop dementia after more than 12 months are classed as having Parkinson’s disease dementia.