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  TABLE 30.3: Common Degenerative Diseases.
Region Affected Disease Main Features Predominant Pathology
I. Cerebral cortex Alzheimer’s disease Progressive senile Cortical atrophy, senile plaques (neurites),
dementia neurofibrillary tangles, amyloid angiopathy
Pick’s disease Pre-senile dementia Lobar cortical atrophy, ballooning degeneration
of neurons (Pick’s cells)
II. Basal ganglia and Huntington’s disease Progressive dementia with Atrophy of frontal lobes, fibrillary astrocytosis
brainstem choreiform movements
Parkinson’s disease Abnormalities of posture Aggregates of melanin-containing nerve cells in
and movement brainstem, intracytoplasmic neuronal inclusions
(Lewy bodies)
III. Spinal cord and Cerebellar cortical Progressive cerebellar Loss of Purkinje cells in cerebellar cortex
cerebellum degeneration ataxia
Olivopontocerebellar Cerebellar ataxia Combination of atrophy of cerebellar cortex,
atrophy inferior olivary nuclei and pontine nuclei
Spinocerebellar atrophy Gait ataxia, dysarthria Degeneration of spinocerebellar tracts,
(Friedreich’s ataxia) peripheral axons and myelin sheaths
IV. Motor neurons Motor neuron disease Syndromes of muscular Progressive loss of motor neurons, both in the
(UMN and LMN) (Amyotrophic lateral weakness and wasting cerebellar cortex (UMN) and in the anterior
sclerosis) without sensory loss horn of spinal cord (LMN)
Werdnig-Hoffmann’s Spinal muscular Loss of lower motor neurons,
disease atrophy in infants denervation atrophy of muscles

and disordered gait and posture. Parkinsonism is caused by A. HEREDITARY METABOLIC DISEASES: CHAPTER 30
several degenerative diseases, the most important being 1. Neuronal storage diseases—characterised by storage of
Parkinson’s disease; other causes of parkinsonism are a metabolic product in the neurons due to specific enzyme
trauma, toxic agents, and drugs (dopamine antagonists).
deficiency. Common examples are: gangliosidoses (e.g.
Tay-Sachs disease or GM2 gangliosidosis), mucopoly-
Grossly, the brain is atrophic or may be normal externally. saccharidoses, Gaucher’s disease and Niemann-Pick
Microscopically, the hallmark is depigmentation of disease). These conditions are described on page 262.
substantia nigra and locus ceruleus due to loss of
neuromelanin pigment from neurons and accumulation 2. Leucodystrophies—are diseases of white matter charac-
of neuromelanin pigment in the glial cells. Some of the terised by diffuse demyelination and gliosis. They are caused The Nervous System
residual neurons in these areas contain intracytoplasmic, by deficiency of one of the enzymes required for formation
eosinophilic, elongated inclusions called Lewy bodies. and maintenance of myelin. That is why these conditions
are also called dysmyelinating diseases. Common types of
leucodystrophies are: sudanophilic leucodystrophy,
Metabolic Diseases adrenoleucodystrophy, metachromatic leucodystrophy and
Metabolic diseases of the CNS result from neurochemical globoid cell leucodystrophy (Krabbe’s disease).
disturbances which are either inherited or acquired. 3. Other inborn errors of metabolism—e.g. Wilson’s
Hereditary metabolic disorders predominantly manifest in disease (hepatolenticular degeneration), glycogen-storage
infancy or childhood and include genetically-determined diseases, phenylketonuria and galactosaemia.
disorders of carbohydrate, lipid, amino acid and mineral B. ACQUIRED METABOLIC DISEASES:
metabolism. Acquired or secondary metabolic diseases are the These include the following:
disturbances of cerebral function due to disease in some other 1. Anoxic-ischaemic encephalopathy
organ system such as the heart and circulation, lungs and 2. Hypoglycaemic encephalopathy
respiratory function, kidneys, liver, endocrine glands and 3. Hyperglycaemic coma
pancreas. In addition, endogenous metabolic diseases may 4. Acute hepatic encephalopathy (Reye’s syndrome)
be caused by toxic injuries induced by metals, gases, 5. Chronic hepatic encephalopathy
chemicals, and drugs. The pathologic changes in each of these 6. Kernicterus
conditions are quite diverse and include oedema, neuronal 7. Uraemic encephalopathy
storage, degenerative changes, and sometimes parenchymal 8. Encephalopathy due to electrolyte and endocrine
necrosis. disturbances.
The predominant types of hereditary and acquired All these conditions have already been discussed in the
metabolic disorders are as under: relevant chapters.