Excerpt from Dementia With Lewy Bodies

Please click here to view the full topic text: Dementia With Lewy Bodies

Background

Frederick Lewy first described Lewy bodies (LBs), cytoplasmic inclusions found in cells of the substantia nigra in patients with idiopathic Parkinson disease (PD), in 1914. In the 1960s, several pathologists described patients with dementia who had LBs of the neocortex. However, such cases were presumed to be rare until the mid 1980s, when sensitive immunocytochemical methods to identify LBs were developed. Dementia with LBs (DLB) was then recognized as being far more common than previously thought.

The relationship of DLB and PD is an area of considerable controversy, particularly because dementia frequently occurs in PD. Many investigators believe that a spectrum of LB disorders exists.

The third report of the DLB Consortium headed by Ian McKeith discusses an arbitrary 1-year rule to distinguish DLB from PD with dementia.¹ If parkinsonism has been present for 12 months or longer before cognitive impairment is detected, the disorder is called PD with dementia; otherwise, it is called DLB. The report recognizes that this rule may be difficult to apply in clinical practice. When dementia precedes motor signs, particularly with visual hallucinations and episodes of reduced responsiveness, the diagnosis of DLB should be considered. Clinical criteria for DLB were first proposed in 1996² and modified in the subsequent DLB Consortium reports³. Several clinicopathological studies have assessed the sensitivity and specificity of these clinical criteria.^{4, 5} These clinical features are discussed below.

Postmortem examinations in both PD and DLB patients demonstrate LBs in the substantia nigra and possibly in the locus ceruleus, dorsal raphe, substantia innominata, and dorsal motor nucleus of the vagus. LBs are found in the neocortex of many patients with idiopathic PD and in all patients with DLB. DLB overlaps parkinsonian dementias.

Pathophysiology

Symptoms and signs of DLB probably result, in part, from disruption of bidirectional information flow from the striatum to the neocortex, especially the frontal lobe. The cause is multifactorial. Altered neuromodulator and/or neurotransmitter levels (eg, acetylcholine [ACh], dopamine) influence the function of many neuronal circuits. In DLB, nonpyramidal cells in layers V and VI of the neocortex may contain LBs. Their function in neocortical information processing and in relaying data to subcortical regions probably is impaired. The etiology of the fluctuations in cognitive function, which characterize DLB, is unknown.

Frequency

United States

Findings from autopsy studies suggest that DLB accounts for 10-20% of dementias. Up to 40% of patients with Alzheimer disease (AD) have concomitant LBs. These mixed cases are sometimes called the LB variant of AD (LBV-AD) and represent an overlap syndrome between DLB and AD. Signs and symptoms of LBV-AD also overlap between DLB and AD. Because the sensitivity and specificity of clinical diagnosis are poor, no good epidemiologic data on incidence or prevalence of DLB are available.

International

Autopsy studies in Europe and Japan indicate that the frequency of DLB is comparable with that reported in studies from the United States.

Mortality/Morbidity

• Dementing illnesses (including DLB) shorten life expectancy.

• With severe disease, patients may experience swallowing problems that can lead to impaired nutrition.

• Patients are at risk for falls because of impaired mobility and balance.

• Because of prolonged bed rest, patients are at risk for decubitus ulcers.

• Dysphagia and immobility also can lead to pneumonia.

Race

DLB has been described in Asian, African, and European races. Data concerning the relative frequency of DLB in different races are not available.

Sex

Most studies suggest that DLB is slightly more common in men than in women.

Age

DLB is a disease of late middle age and old age.

Please click here to view the full topic text: Dementia With Lewy Bodies