Causes and pathogenesis of impaired consciousness

The causes of disorders of consciousness are extremely diverse. According to pathogenesis, all disorders of consciousness are divided into organic, metabolic and psychogenic.

• Organic brain lesions capable of leading to impaired consciousness up to a comatose state include virtually all known primary and secondary diseases and pathological conditions of the central nervous system, both focal and diffuse. First of all, they include acute brain lesions leading to its destruction and compression: craniocerebral trauma, ischemic stroke, intracranial hemorrhages of various etiologies (intracerebral, subdural and epidural hematomas, intraventricular, subarachnoid hemorrhages). Particularly dangerous are acute processes with primary damage to the brain stem (hemorrhages and infarctions of the brain stem), as well as processes accompanied by extensive unilateral or bilateral damage to the cerebral hemispheres or subtentorial structures, since they can quickly lead to the development of brain dislocation with secondary damage to the brain stem. Development of comatose states may be caused by undiagnosed in time space-occupying formations of supra- and subtentorial structures (tumors, brain abscesses). Impaired consciousness may be caused by diseases that lead to diffuse damage to the substance and membranes of the brain: demyelinating diseases, specific and non-specific encephalitis, encephalomyelitis, leptomeningitis, vasculitis. Almost all disorders of consciousness caused by organic pathology of the central nervous system can be accompanied by certain focal symptoms indicating the localization of the primary or secondary lesion: meningeal symptoms, cranial nerve damage, pyramidal, extrapyramidal, and brainstem symptoms.
• Metabolic factors leading to disorders of consciousness constitute a large group. In general, they can be divided into internal and external, or endo- and exotoxic. In a number of situations, such a division can be quite arbitrary. The causes of endogenous intoxications are:
  • - pathology of internal organs leading to conditions such as liver and kidney failure (uremia), eclampsia of pregnant women;
  • dysfunction of the endocrine glands: diabetes mellitus (hypo- and hyperglycemic coma), adrenal insufficiency, thyrotoxicosis, hyperparathyroidism;
  • severe vitamin deficiency (thiamine, folic acid, B ₁₂, etc.);
  • water-electrolyte imbalance (hypo- and hyperosmolar coma), including damage to the pituitary gland (pituitary coma), acid-base imbalance (respiratory or metabolic acidosis or alkalosis), anemia, severe bacterial and viral infections, cancer intoxication, anaphylactic shock, etc.

A special place among metabolic disorders is occupied by conditions leading to hypoxia and anoxia of the brain: anoxic anoxia (oxygen for one reason or another does not enter the blood in the required quantities), anemic anoxia (reduced hemoglobin content), ischemic anoxia (conditions leading to a rapid general decrease in cerebral blood flow: decreased cardiac output during myocardial infarction, arrhythmia, asystole, vasodepressor reactions in shock states, etc.). External influences include, first of all, various medications (barbiturates, tranquilizers, narcotics, antidepressants, salicylates, etc.), toxic substances (alcohol, methyl alcohol, natural and industrial poisons, carbon monoxide), alimentary factors (alimentary-dystrophic coma), hypo- and hyperthermia (heat stroke). A common feature of all metabolic disorders of consciousness is the comparative paucity of focal neurological symptoms, even in patients in a coma.

• Psychogenic disorders in rare cases can manifest as complete unresponsiveness. This condition can occur with hysteria, severe depression, schizophrenia. Psychogenic unresponsiveness is characterized by normal somatic and neurological status with preservation of all physiological reflexes, absence of changes in laboratory tests, and practically normal EEG.

The rate of development and duration of disorders of consciousness vary. The disease may begin with a sudden complete loss of consciousness (brainstem hemorrhage, ventricular hemorrhage) or it may be preceded by a period of prolonged, often wave-like changes in consciousness such as blackout or confusion (endogenous intoxications), an episode of psychomotor agitation (hypoxia, craniocerebral trauma), an epileptic seizure (epilepsy, cerebrovascular accident), or the development of focal symptoms (stroke, tumor). Disorders of consciousness may be short-term (fainting, absences) or indefinitely prolonged. The latter mainly refers to profound depression of consciousness. Prolonged disorders of consciousness are usually called chronic. Chronic disorders, as a rule, are the outcome of a comatose state. It is proposed to consider a period of 2-4 weeks as the criterion for the transition of an acute disorder of consciousness to a chronic one.

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