LEWY BODY PATHOLOGY
A group of closely
related neurodegenerative diseases characterised by the formation of intracytoplasmic
neuronal inclusions, the lewy body.
1. Idiopathic Parkinson's disease
In typical cases
the only macroscopical abnormality is the pallor of the pigmented nuclei of the
brainstem: the substantia nigra and locus coeruleus. Usually there is no
diffuse atrophy, the presence of this indicates Alzheimer's disease or diffuse lewy
body diaease.
The following are
the histological features:
a.
The hallmark
lesion of idiopathic Parkinson's disease is the Lewy body. These are intracytoplasmic
neuronal inclusions which are intensely eosinophilic with routine
haematoxylineosin stain. They occur in the pigmented nuclei of the brainstem:
in the substantia nigra and locus coeruleus, as well as in the motor nucleus of
the vagus, in the nucleus basalis of Meynert, in the spinal cord and in
sympathetic ganglia. Their structure and composition vary in different parts of
brain; in the brainstem they have a clearly defined halo which is usually
absent from the cortical inclusions. Ultrastructurally they are chiefly
composed of filaments with greatest central density known as the core.
b.
Immuoocytocbemically,
they share epitopes with phosphorylated and non-phosphorylated neurofilament
subunits, tubulin, microtubule-associated protein 1 and 2, and they positively
immunostain with ubiqiutin.
c.
Neuronal
loss occurs in the substantia nigra and locus coeruleus, as a consequence there
is extraneuronal pigment in the neuropil and in macrophages. In severe cases, this
neuronal loss is accompanied by astrocytosis, best demonstrated by immunocytochemistry
for glial fibrillary acidic protein (GFAP). Neuronal loss also occurs
elsewhere, including the nucleus basalis of Meynert.
d.
Changes in
the globus pallidus and putamen are less severe and less constant than those in
the pigmented nuclei of the brainstem.
2. Diffuse Lewy body disease
Lewy bodies have
been noted in the cortex, resulting in the definition of diffuse lewy body
disease. They usually occur in large numbers in the parahippocampal gyrus,
cingulate and insular cortices, but also throughout the neocortex, well in excess
of the occasional cortical inclusions in idiopathic Parkinson's disease. This
diffuse distribution of lewy bodies is often associated neuropathologically
with Alzheimer type changes, mainly with plaque formation, and clinically with
dementia. Cortical Lewy bodies are more difficult to discern than the brainstem
inclusions, since they usually lack the distinct peripheral halo. They are most
often seen in the deeper, 5th and 6th cortical layers, but also occur in layers
2 and 3.
As distinct from
difuse Lewy body disease, a clinically and neuropathologically defined form of
Lewy body dementia has been described recently in the elderly: senile dementia
of the Lewy body type. Clinically these cases do not fulfill the diagnostic
criteria of either Alzheimer's or Parkinson's disease. Neuropathology shows
Lewy body formation and selective neuronal loss in the brainstem and other
subcortical nuclei, and Lewy bodies in the neocortex and limbic cortex, but at
a frequency well below that reported for diffuse Lewy body disease. Senile
plaques are common, whilst tangles are rare; the plaques tend to be the diffuse
type without neuritic component. These cases are similar to those reported as
Lewy body variant of AIzheimer's disease, characterised by cortical and
subcortical Lewy bodies, senile plaque formation and spongiform vacuolation of
the temporal cortex.