Pathological processes in neurology

Published on 09/04/2015 by admin

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Last modified 09/04/2015

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Pathological processes in neurology

It is useful to appreciate the ways in which the nervous system malfunctions. This is important clinically because the time course of any pathological process is described by the patient in the history. It also provides a framework for understanding different types of disease, particularly rarer diseases that you might not otherwise know about.

Broadly, pathological processes can be divided into (Fig. 1):

Systemic – abnormalities in the nervous system secondary to systemic disease.

Intrinsic – arising within the nervous system.

Vascular – resulting from disturbances in the blood supply to the nervous system.

Extrinsic – affecting the nervous system from outside.

Fig. 1 Four types of pathological processes.

Hint: remember this as SIVE. There is some overlap between these categories.

Systemic

These changes are usually due to metabolic, toxic, nutritional, immunological or endocrine disorders (Table 1).

Table 1 Systemic processes

Disorder	Clinical syndrome
Metabolic	Hypo- or hyperglycaemia, hyponatraemia, hypoxia, hypercarbia, hyper- or hypocalcaemia Renal failure Liver failure Wilson’s disease

}Metabolic encephalopathy
Extrapyramidal syndrome Toxic

Organic solvents

Nutritional

Vitamin B12 deficiency

Thiamine deficiency

Neuropathy, myelopathy Neuropathy, Wernicke–Korsakoff encephalopathy Endocrine

Hyperthyroidism

Addison’s disease

}Myopathy

Metabolic

The function of the nervous system requires appropriate systemic homeostasis. If disrupted, this commonly produces a metabolic encephalopathy, with confusion or coma as seen in hypoglycaemia or hyponatraemia. The neurological manifestations may overshadow the other features of these metabolic disturbances.

Other metabolic changes produce more insidious nervous system damage. For example, diabetes mellitus causes peripheral neuropathies, more often if glycaemic control is poor. The gradual accumulation of copper in Wilson’s disease produces psychiatric disturbances and a Parkinsonian syndrome.

Toxic

Neurotoxins can affect the central or peripheral nervous system. The most common neurotoxin is alcohol; others include drugs, heavy metals, organic solvents and rarer ‘designer’ drugs. These substances can produce acute neurological illnesses or subacute or chronic illnesses. Some effects of drugs are common: for example, the extrapyramidal syndromes seen with antipsychotic agents and the cerebellar syndromes seen with phenytoin or carbamazepine toxicity.

Nutritional

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