Metabolic Encephalopathies

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Metabolic encephalopathy describes a clinical state of heterogeneous etiology; wherein, cerebral activity is impaired in the absence of parenchymal inflammation or gross structural abnormalities. Metabolic encephalopathy is not a diagnosis but a state of global cerebral dysfunction induced by systemic stress, and can vary in clinical presentation from mild executive dysfunction, to an agitated delirium, to deep coma with decerebrate posturing. This chapter focuses on common causes of metabolic encephalopathy, and outlines the epidemiology, clinical presentation, laboratory and imaging findings, and management. The chapter gives an account for hepatic encephalopathy, uremic encephalopathy, posterior reversible leukoencephalopathy syndrome, pulmonary encephalopathy, pancreatic encephalopathy, and Hashimoto's encephalopathy. Thyroid hormones also act at the level of the mitochondrion to stimulate oxidative metabolism. They also act on the cell membrane to affect the sodium–potassium pump. Adrenal failure is a medical emergency related to a deficiency of adrenal cortical hormones. Electrolyte disturbances are common causes of metabolic encephalopathy. The chapter also describes encephalopathies related to the disruption of sodium, calcium, magnesium, phosphate, and glucose homeostasis.

Section snippets

Hepatic encephalopathy

Hepatic encephalopathy (HE) is a potentially reversible neuropsychiatric clinical syndrome stemming from acute or chronic liver failure. Acute liver failure, a manifestation of impaired hepatocellular function, begins within 6 months from the onset of liver disease. Fulminant hepatic failure is a subset of acute liver failure and is a particularly catastrophic condition, characterized by rapid onset of hepatic encephalopathy, coagulopathy from hepatocellular dysfunction, and cerebral edema, and

Uremic encephalopathy

Impairment of consciousness and other CNS abnormalities associated with kidney failure can be broadly categorized into those related to kidney failure per se and those resulting from the treatment of renal failure. Uremia is the clinical syndrome of renal failure, and its full expression is manifested in the context of multiple organ system dysfunction. Uremia is caused by two main mechanisms: 1) excessive accumulation of products of protein metabolism; and 2) loss of intrinsic kidney

Posterior reversible leukoencephalopathy syndrome

Coined by Hinchey et al. (1996), the posterior reversible leukoencephalopathy syndrome (PRLE or PRES; sometimes called reversible posterior leukoencephalopathy (RPL)) is a relatively recently described metabolic encephalopathy. In its initial description, patients with hypertension associated with renal disease, pre-eclampsia, or immunosuppressant therapy developed a syndrome of headache, altered mental status (from confusion to stupor or coma) and a variable combination of vomiting, seizures,

Pulmonary encephalopathy

Plum and Posner coined the term pulmonary encephalopathy – an encephalopathic state due to respiratory insufficiency often from mixed etiologies including hypoxemia, hypercapnia, respiratory exhaustion or fatigue, systemic infection, or congestive heart failure. Retention of CO2 is the most common cause of the pulmonary encephalopathy, since its level most closely follows the CNS disturbance (Austen et al., 1957), although isolated hypoxia will also lead to impaired consciousness. Pulmonary

Pancreatic encephalopathy

Pancreatic encephalopathy is a rare and controversial CNS complication of pancreatitis with fewer than 30 reports in the literature.

Hashimoto's encephalopathy

Lord Brain described an unusual case of a 40 year old man with a previous diagnosis of autoimmune thyroiditis who had multiple episodes of alternating hemiplegia, with visual disturbances and protracted confusional states associated with abnormal EEG, elevated thyroid antibodies, and normal thyroid function. The patient fully recovered with normalization of his laboratory findings (Brain et al., 1966). According to Brain, ‘The association of the two disorders – the thyroiditis and the brain

Actions of thyroid hormone

Thyroid hormones (thyroxine (T4) and triiodothyronine (T3)) bind nuclear receptors (TRs) in cells; in the brain these are mainly TRα receptors. TRs are present in most brain regions, including cerebral neocortex, hippocampus, thalamus, hypothalamus, cerebellum, and brainstem nuclei (Constantinou et al., 2005). Thyroid hormones play an important role in the maturation of the brain in all mammals. Genes regulated by thyroid hormone have been identified in neurons, astroglia, and oligodendrocytes,

Acute adrenal failure

Adrenal failure is a medical emergency related to a deficiency of adrenal cortical hormones. Primary adrenal cortical failure affects both cortisol and aldosterone secretion, while secondary adrenal failure affects only cortisol secretion. Cortisol secretion is under the direction of the hypothalamic–pituitary axis while aldosterone is regulated by the renal–adrenal axis.

Cortisol acts on a cytoplasmic receptor; the cortisol–receptor complex moves into the cell nucleus to bind to specific DNA

Electrolyte disturbances

Electrolyte disturbances are common causes of metabolic encephalopathy. Disruption of electrolyte balance is invariably secondary to other processes, whether iatrogenic or due to impairment of the organ function that regulates the particular electrolyte homeostasis. This section focuses on encephalopathies related to the disruption of sodium, calcium, magnesium, phosphate, and glucose homeostasis.

Idiopathic recurrent stupor: endozepine stupor

This rather curious syndrome is characterized by recurrent spontaneous stupor with associated fast EEG (beta frequency) that is responsive to the GABAA antagonist flumazenil.

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