LA DIMENSIÓN COMO VECTOR DE CAMBIO. ESTRATEGIAS DE CRECIMIENTO

paramyotonia congenita. In the former condition (due to chloride transport abnormality) the symptoms improve with exercise, while the latter condition (due to sodium channelopathy) worsens with exercise and with cold. Needle insertion into muscles usually easily identifies myotonic potentials.

2. Periodic paralysis: These are thyrotoxic periodic paralysis and familial periodic paralysis (hypo-, hyper-, or normokalemic and Andersen syndrome). These often produce generalized and temporary weakness after large meals or exercise. Diagnosis can be made by provoking the weakness by a glucose load and exercise.

Myotonias and periodic paralyses are rare and are recognized clinically. Electromyography may show typical myotonic discharges. Treatment of symptoms and avoidance of precipitating factors may be helpful in both groups.

References

● Brooke, M.H.: A Clinician's View of Neuromuscular Diseases. Baltimore, Williams & Wilkins Co.,

1977.

● Dyck, P.J., Thomas, P.K., Lambert, E.H.: Peripheral Neuropathy, Philadelphia, W.B. Saunders

Co., 1975.

● Engle, E.J., Banker, B.Q.: Myology. New York, McGraw-Hill, 1986.

● Walton J.N.: Disorders of Voluntary Muscle, ed. 4, New York, Churchill Livingston, 1981.

Questions

Define the following terms:

neuropathy, myopathy, neuromuscular junction/myoneural disease, "dying back",

demyelinative, Wallerian degeneration, epineurium, perineurium, endoneurium, Schwann cells, myelin, entrapment neuropathy, carpal tunnel, lateral femoral cutaneous neuropathy/

meralgia paresthetica, polyneuropathy, Charcot-Marie Tooth, Lambert-Eaton myasthenic syndrome, paraneoplastic syndrome, myasthenia gravis, nerve conduction study,

electromyography.

12-1. What modalities are conveyed by large, myelinated nerve fibers?

12-2. What do small-diameter sensory nerve fibers convey.

12-3. What is entrapment neuropathy?

12-4. What are symptoms of polyneuropathy?

12-5. What are the causes of polyneuropathy?

12-6. What are the potential causes of myopathy?

12-7. What are the common symptoms of myopathy?

12-8. What effect do myopathies have on reflexes?

12-9. What additiional test would point to myopathy as a cause of weakness?

12-10. What is the most common neuromuscular/myoneural junction disease?

12-11. Who is most often affected by myasthenia gravis?

12-12. What are the symptoms of myasthenia gravis?

12-13. What blood test may be helpful in diagnosis

12-14. What is the common distribution of symptoms in the body?

12-15. What is the treatment for myasthenia gravis?

12-16. What is Lambert-Eaton myasthenic syndrome?

12-17. What is the function of nerve conduction studies?

12-18. What does electromyography evaluate?

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Disorders of the Nervous system - Reeves & Swenson

Epilepsy is "an occasional, an excessive and a disorderly discharge of nervous tissue" (John Hughlings Jackson, 1889) induced by any process involving the cerebral cortex that pathologically increases the likelihood of depolarization and synchronized firing of groups of neurons. There are many potential underlying causes including metabolic disorders of nerve cells or virtually any disorder that damages cortical tissue including trauma, hemorrhage, ischemia, anoxia, infection, or hyperthermia, as well as the presence of scar tissue relating to prior injury.

All neurons in the nervous system are capable of excessive firing when

damaged; however, the threshold for this abnormality varies considerably in different areas. The cerebral cortex is the only area from which epileptiform activity arises with any frequency. Not all areas of the cerebral cortex have the same tendency to epileptic activity: most of the neocortex is relatively resistant, while the temporal lobes and frontal lobes (particularly the limbic areas) are highly susceptible.

Electrodes applied to the scalp (the electroencephalogram; EEG) are often able to detect abnormal activity of a seizure. The excessive

electroencephalographic discharge recorded can be useful in localizing the

Go!

seizures

source of the seizure activity and occasionally by its pattern can delineate the type of seizure disorder. It is unusual to have the opportunity to record an EEG during the actual clinical seizure. However, up to 2/3 of patients have abnormal electrical discharges that can be recorded between clinical events.

A normal EEG in a person suspected of having epilepsy does not rule out the possibility since inter-seizure (interictal) electric activity is frequently normal.

It is important to note the distinction between seizures and "epilepsy" (often called a "seizure disorder"). A seizure is an event. All human cerebral cortices

have the potential to generate seizures given enough of a stimulus. In fact, nearly 10 percent of people will have one at some time in their life. However, the term epilepsy implies an abnormally heightened tendency to have seizures such that the person is likely to have them in the course of normal life from time-to-time. This can range from one a decade to many in a day.

There are several types of seizures. Broadly, they can be divided into primary generalized seizures and focal onset (localization-related) seizures. In primary generalized seizures, the seizure involves all of the cerebral cortex simultaneously. In focal onset seizures, it involves a localized cluster of neurons having epileptiform activity. Table 13-1 presents a simplified functional-anatomical categorization of seizure types. It is not exhaustive but it does give the spectrum of major seizure categories. While most seizures present with motor correlates, some can present with mainly inhibitory phenomena. The blank, staring episodes of petit mal, the common childhood seizure disorder, are a good example.

Seizures are not only recognized by the activity during the main portion of the seizure but also by

phenomena that lead up to the clinical seizure (often termed an "aura"), and the condition of the patient after the event (the "post-ictal" state).