Porth's Essentials of Pathophysiology, 4e

913

Disorders of Neuromuscular Function

C h a p t e r 3 6

skin integrity are pressure, shearing forces, and local- ized trauma and irritation. Relieving pressure, allowing adequate circulation to the skin, and skin inspection are primary ways of maintaining skin integrity. Of all the complications after SCI, skin breakdown is the most preventable. Future Directions in Repair of the Injured Spinal Cord There is a continued effort to determine new and innovative strategies for repairing the injured spinal cord. 7,67–71 At present, these strategies focus on pro- moting the regrowth of interrupted nerve fiber tracts, using nerve growth–stimulating factors or molecules that suppress inhibitors of neuronal extension; bridg- ing spinal cord lesions with scaffolds that are impreg- nated with nerve growth factors, which promote axon growth and reduce the barriers caused by scar tissue; repairing damaged myelin and restoring nerve fiber conductivity in the lesion area; and enhancing CNS plasticity by promoting compensatory growth of spared, intact nerve fibers above and below the level of injury. Stem cell transplantation offers a promis- ing therapeutic strategy for spinal cord injury repair. 68 Although these strategies may not allow for complete repair of the spinal cord or to recreate what was pres- ent before the injury, even small successes may be use- ful for someone with SCI. ■■ Upper motor neuron (UMN) lesions are those involving neurons completely contained in the central nervous system (CNS). ■■ Amyotrophic lateral sclerosis is a progressive and devastating neurologic disorder that selectively affects motor function. It affects lower motor neurons (LMNs) in the spinal cord as well as UMNs in the brain stem and cerebral cortex. ■■ Multiple sclerosis is a slowly progressive demyelinating disease of the CNS that is characterized by exacerbations and remissions of paresthesias, optic neuritis, and motor weakness. ■■ Spinal cord injury (SCI) is a disabling neurologic condition of UMNs in the spinal cord that produces various degrees of sensorimotor loss and altered reflex activity based on the level of injury and extent of cord damage. Depending on the level of injury, SCI is associated with ventilation and communication SUMMARY CONCEPTS

R E V I EW E X E R C I S E S 1. A 32-year-old woman presents with complaints of “drooping eyelids,” difficulty chewing and swallowing, and weakness of her arms and legs that is less severe in the morning but becomes worse as the day progresses. She complains that climbing stairs and lifting objects are becoming increasingly difficult. Clinical examination confirms weakness of the eyelid and jaw muscles. She is told that she may have myasthenia gravis and is scheduled for testing using the short-acting acetylcholinesterase inhibitor edrophonium (Tensilon). A. Explain the pathogenesis of this woman’s symptoms as it relates to myasthenia gravis. B. Explain how information from the administration of the acetylcholinesterase inhibitor edrophonium can be used to assist in the diagnosis of the disorder. 2. A 20-year-old man suffered spinal cord injury at the C2 to C3 level as the result of a motorcycle accident. A. Explain the effects of this man’s injury on ventilation and communication; sensorimotor function; autonomic nervous system function; bowel, bladder, and sexual function; and temperature regulation. B. Autonomic dysreflexia, which is a threat to persons with spinal cord injuries at T6 or above, is manifested by hypertension, often to extreme levels, and bradycardia; constriction of skin vessels below the level of injury; and severe headache and nasal stuffiness. Explain the origin of the elevated blood pressure and bradycardia. The condition does not occur until spinal shock has resolved, and usually occurs only in persons with injuries at T6 and above. Explain. problems; autonomic nervous system dysfunction that predisposes to the vasovagal response, autonomic hyperreflexia, impaired body temperature regulation, and postural hypotension; impaired muscle pump and venous innervation leading to edema of dependent areas of the body and risk for deep vein thrombosis; altered sensorimotor integrity that contributes to uncontrolled muscle spasms, altered pain responses, and threats to skin integrity; alterations in bowel and bladder elimination; and impaired sexual function.