Answers

447. The answer is b. (Victor, pp 768-770.) The clinical scenario presented is most consistent with a neuropathy of Lyme disease, the infection caused by Borrelia burgdorferi. This spirochetal infection is tick-borne and is endemic in the area where this patient lives. The rash on his leg was most likely erythema chronicum migrans, a target-shaped lesion that enlarges as the central area returns to normal. His complaints and examination suggest a chronic meningitis preceded by an arthralgia, a common neurologic scenario with Lyme disease. Facial weakness may be the only neurologic sign of Lyme disease. The neurologic deficits usually appear weeks after the initial rash. Untreated neurologic disease may persist for months. Optic neuritis may also appear in association with the chronic meningitis of Lyme disease. A schwannoma may develop on the seventh cranial nerve, but it would produce unilateral facial weakness followed by signs of brainstem compression. The cranial nerve dysfunctions associated with the early stages of diphtheritic polyneuropathy are a consequence of a toxin released by the infectious agent. Tuberculous meningitis may produce several different cranial nerve deficits. With HIV infection, a peripheral neuropathy may develop, but it typically affects the limb nerves, not the facial nerve.

448. The answer is e. (Victor, p 1223.) These antituberculous drugs should be supplemented with pyridoxine to avoid a relative pyridoxine deficiency elicited by the isoniazid. The peripheral neuropathy evoked by the antituberculous agent will appear initially as disturbed sensation in the distal limbs. Paradoxically, pyridoxine overdose may also elicit a peripheral neuropathy, but overdose sufficient to produce a peripheral neuropathy is usually only seen in persons taking many times the recommended daily allowance of pyridoxine in vitamin preparations. It does not develop from eating foods with high levels of pyridoxine. Excessive pyridoxine consumption is usually linked to hypochondriasis or compulsive behavior. Ceftriaxone and erythromycin are appropriate antibiotics in the management of Lyme diseases. The cephalosporin is preferred unless the patient is intolerant of that class of antibiotics.

449. The answer is a. (Victor, pp 1393-1394.) This patient has, in effect, developed a noncompressive sciatica, or Lyme neuropathy. Dorsiflexion of the foot is controlled primarily by the anterior tibial muscle. The deep peroneal nerve supplies this muscle and arises from the common peroneal nerve just below the knee. A sciatic nerve injury may also produce foot-drop, and irritation of spinal roots to the sciatic nerve produces the foot-drop that may occur with Lyme radiculopathy. Lyme disease causes painful radiculopathies and peripheral neuropathies. Tuberculosis may cause similar complaints, but steroid therapy is often useful in suppressing that complaint in chronic tuberculous meningitis. Steroid-induced diabetes mellitus would be unlikely to evolve to the point that a painful neuropathy developed over so short a time.

450. The answer is c. (Victor, p 287.) Aberrant regeneration of a cranial nerve is not all that uncommon, but it is more often seen after injury to the third nerve than to the seventh. For unknown reasons, the regenerating motor fibers miss their original targets and innervate new destinations. With cranial ALS, facial twitching occurs, but it is not preceded by unilateral weakness; and it is seen as the weakness evolves, not as it remits. Sar-coidosis may produce facial weakness with aberrant regeneration, but this patient's history does not suggest this idiopathic granulomatous disease. There is nothing to suggest that his Lyme disease is recurring, although recurrent meningitis may develop with inadequate treatment.

451. The answer is e. (Victor, p 49.) Myotactic, or tendon stretch, reflexes require intact sensory supplies from the tendons and motor supplies to the muscles involved. The patellar tendon reflex entails contraction of the quadriceps femoris muscle group, a muscle group with four members: the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. This reflex requires perception of stretch in the tendon stretch receptors innervated by L2 and L3. With tapping of the tendon that extends from the patella to the head of the tibia, spinal reflex pathways activate contraction of the quadriceps femoris group and evoke extension of the lower leg with straightening of the knee. Damage to the motor supply to the reactive muscles must be profound before the tendon reflex will be lost completely. Corticospinal tract damage will produce hyperreflexia, apparently by disin-hibiting spinal cord mechanisms.

452. The answer is a. (Victor, pp 1393-1394.) Lead poisoning, especially in adults, produces a painless neuropathy often targeting the radial nerve and resulting in a wristdrop. Lead poisoning in children is likely to produce increased intracranial pressure and cognitive dysfunction. Thallium poisoning may produce hair loss, stupor, gastrointestinal distress, seizures, and headaches, as well as a painful, symmetric, primarily sensory neuropathy. Manganese is also a toxin, but long-term exposure to this metal may produce parkinsonism rather than a sensory neuropathy. Cyanide was long regarded as the cause of an optic neuropathy, but this lethal toxin has probably been unjustly ascribed this capability. Mercury poisoning may produce a sensory neuropathy, but it is generally associated with paresthesias, rather than dysesthesias.

453. The answer is a. (Victor, pp 1396-1399.) Diabetes mellitus is the most common cause of mononeuropathy multiplex. In this disorder, individual nerves are transiently disabled. The neuropathy usually develops over the course of minutes to days, and the recovery of function may require weeks to months. Various rheumatoid diseases and sarcoidosis produce similar clinical pictures, but temporal arteritis does not typically lead to this type of neuropathy. A vascular lesion is believed to be the most common basis for this type of neuropathy. If the giant cell arteritis seen with temporal arteritis does cause a neuropathy, it is an optic neuropathy with resultant blindness. Unlike the peripheral nerve injuries that develop with mononeuropathy multiplex, this ischemic optic neuropathy of temporal arteritis produces irreversible injury to the affected cranial nerve. The patient who loses vision as part of temporal arteritis does not recover it.

454. The answer is a. (Victor, p 1428.) The radial nerve supplies the extensors of the wrist and derives from the posterior cord of the brachial plexus. The brachial plexus arises from C5, C6, C7, C8, and T1. These spinal roots form the trunks of the brachial plexus. C5 and C6 form the upper trunk; C7, the middle trunk; and C8 and T1, the lower trunk. The trunks in turn divide into anterior and posterior divisions, which associate into cords: the anterior division of the upper and middle trunks gives rise to the lateral cord; the posterior divisions of all the trunks give rise to the posterior cord; and the anterior division of the lower trunk gives rise to the medial cord.

455. The answer is c. (Victor, p 1428.) The upper brachial plexus includes the fifth and sixth cervical spinal roots. Damage to these roots occurs during a difficult birth if the head and the shoulder are forced widely apart. This could result in stretching or even avulsion of these cervical spinal roots from the spinal cord. Node dissection in the axilla or a Pancoast tumor at the apex of the lung may produce brachial plexus injury, but it is the lower plexus that is vulnerable. Dislocation of the head of the humerus or aneurysm of the sub-clavian artery will typically injure the cords of the brachial plexus, the final elements of the plexus from which the principal nerves of the arm arise.

456. The answer is d. (Rowland, p 645.) Degeneration occurs primarily in the spinal cord rather than the cerebellum or brainstem in patients with Friedreich's disease. Both the dorsal and ventral spinocerebellar tracts are involved. The other spinal cord structures exhibiting degeneration include the posterior columns and the lateral corticospinal tracts.

457. The answer is b. (Rowland, p 646.) More than 10% of patients with Friedreich's disease develop diabetes mellitus. A more life-threatening complication of this degenerative disease is the disturbance of the cardiac conduction system that often develops. Visual problems occur with the hyperglycemia of uncontrolled diabetes mellitus, but even Friedreich's patients without diabetes develop optic atrophy late in the course of the degenerative disease.

458. The answer is a. (Rowland, pp 645-646.) Degenerative changes in the peripheral nerves of patients with Friedreich's disease have several bases. Loss of cells in the dorsal root ganglia makes a major contribution to this phenomenon. Additional sites of degeneration that affect the sensory system include the substantia gelatinosa (Lissauer's tract) of the posterior horn and the dorsal roots themselves. The peripheral neuropathy is responsible for the hyporeflexia that is invariably found in the legs of affected persons.

459. The answer is b. (Rowland, p 645.) Spinocerebellar atrophy does occur linked to chromosome 6, but this is distinct from Friedreich's ataxia. The site of the mutation responsible for Friedreich's ataxia has been identified on chromosome 9, and the gene product, the protein frataxin, has been identified. Friedreich's disease is inherited as an autosomal recessive defect.

460. The answer is b. (Rowland, pp 645-646.) Congenital abnormalities are rarely evident with Friedreich's disease, but kyphoscoliosis, pes cavus, and other musculoskeletal abnormalities may become evident quite early in childhood. Gait difficulty usually develops during childhood in persons with Friedreich's disease. Visual loss, syncope, vertigo, and dysarthria may develop during the course of this degenerative disease, but the appearance of these other problems may be decades after that of the gait ataxia. Visual loss may develop with optic atrophy or retinitis pigmentosa. Strictly cere-bellar or spinocerebellar tract signs include limb ataxia, nystagmus, dysarthria, and gait difficulty. Systemic problems often found in persons with Friedreich's disease include diabetes mellitus and cardiac conduction defects.

461. The answer is b. (Victor, p 1382.) This patient's clinical course is consistent with a diagnosis of AIDP, also known as Guillain-Barre syndrome. Cerebrospinal fluid is typically under normal pressure in this syndrome, and contains no cells in up to 90% of patients. In 10% of patients, 10 to 50 WBCs, mostly lymphocytes, may appear. Protein levels are generally elevated, sometimes to extremely high levels, reflecting the degree of inflammatory activity taking place at the level of the spinal roots.

462. The answer is e. (Victor, pp 1382-1383.) Serologic studies have shown that C. jejuni is the most common infection preceding Guillain-Barre syndrome. Other less common infections include viral illnesses such as CMV HIV, and Epstein-Barr virus, Lyme disease, and M. pneumoniae infection. Guillain-Barre syndrome has also been associated with surgical procedures, exposure to thrombolytic agents, lymphoma, and certain vaccines.

463. The answer is c. (Victor, pp 1385-1386.) Treatment of Guillain-Barre syndrome is complicated and is best accomplished in an experienced center. Specific therapies include plasma exchange and intravenous immunoglobulin, which appear to be equivalent in several recent studies. When instituted early (within 2 weeks of symptom onset), these modalities can reduce the period of hospitalization, the length of time on mechanical ventilation, and the time to begin walking again. Corticosteroids do not appear to be of benefit. The role of other immunosuppressants, such as cyclophosphamide, has not been evaluated. 3,4-diaminopyridine is used in the treatment of Lambert-Eaton myasthenic syndrome.

464. The answer is d. (Victor, pp 1427-1428.) Parsonage-Turner syndrome refers to an acute brachial plexopathy. It may also be called brachial neuritis or neuralgic amyotrophy. Usually it begins with acute onset of pain in the neck, shoulder, or upper arm. This is followed 3 to 10 days later by the rapid evolution of weakness affecting the proximal muscles of the arm; rarely, the hand or the respiratory muscles may also be affected. Sensory loss also occurs. Some cases are bilateral. Usually, systemic signs are absent, though mild pleocytosis may occur. The cause is unknown, but the occurrence of the syndrome after vaccination or viral infection has led to the notion that it is an immunological or autoimmune response of some sort. Familial cases also occur with an autosomal dominant pattern.

465. The answer is c. (Victor, p 1423.) Familial dysautonomia, or Riley-Day disease, is an autosomal recessive disorder that affects primarily Jewish children. It is characterized by a small-fiber neuropathy affecting both myelinated and unmyelinated small fibers, thereby causing an impairment of pain and temperature sensation. Sympathetic and parasympathetic ganglia are also affected, causing the autonomic features. The autonomic manifestations may include loss of tears on crying, corneal ulceration, absence of pupillary reactivity, poor temperature regulation, excessive perspiration, abnormalities of blood pressure control, dysphagia, recurrent vomiting, and gastric and intestinal dilation. There is absence of the papillae of the tongue. There is no effective treatment other than symptomatic.

466. The answer is f. (Victor, pp 1410-1413.) Chronic inflammatory demyelinating polyneuropathy (CIDP) is similar to Guillain-Barre syndrome, but it takes a slowly progressive or remitting course rather than one of acute onset and rapid resolution. It is a polyradiculoneuropathy, implying that it affects the proximal portions of the nerves where they exit the spinal cord at the root level. This is the reason for the increase in protein, indicating an inflammatory disorder affecting nerve roots and causing demyelination. Because nerve roots are affected, this chronic neuropathy is not limited at onset to the distal feet, as a diabetic or other degenerative neuropathy might be. Patients therefore experience paresis and sensory loss proximally as well as distally.

467. The answer is g. (Victor, pp 1389-1390.) Porphyric polyneuropathy is associated with acute intermittent porphyria, which is a disorder of heme biosynthesis in the liver resulting from increased production and excretion of porphobilinogen and S-aminolevulinic acid. The skin is not abnormal in this disorder. Instead, it is characterized by recurrent attacks of abdominal pain, gastroparesis and constipation (due to autonomic neuropathy), psychosis, axonal motor neuropathy, and autonomic instability. Seizures and syndrome of inappropriate antidiuretic hormone (SIADH) may also occur. Attacks may be fatal if respiratory paralysis or cardiac arrest occurs. Attacks may be provoked by porphyrinogenic drugs, such as barbiturates, pheny-toin, sulfonamide antibiotics, and estrogens. These should be avoided in such patients. Treatment is best accomplished with use of intravenous hematin when supportive measures are not adequate or the case is severe.

468. The answer is f. (Bradley, p 2119.) Peripheral neuropathy from exposure to anesthetic agents is an occupational hazard faced by many health care providers. Megaloblastic anemia may develop along with peripheral neuropathy in nitrous oxide-induced neuropathy This hazard is greatly increased if the health care worker uses the anesthetic agent as a recreational drug, which is a relatively common practice with nitrous oxide. Substance abuse involving agents intended for only occasional or short-term use, such as anesthetic agents, opiates, and opioids, must be rigorously explored with health professionals who develop inexplicable neurologic syndromes. Long-term abuse of nitrous oxide may lead to numbness, paresthesias, limb spasticity, and ataxia, signs pointing to central, rather than peripheral, nervous system damage. The syndrome is difficult to distinguish from vitamin B12 deficiency, and appears to result from interference with the vitamin B12-dependent conversion of homocysteine to methionine.

469. The answer is b. (Rowland, p 621.) Early in its evolution, sarcoid may be misconstrued as MS, especially if all the obvious deficits can be traced to the CNS. Optic atrophy and facial nerve palsies are common in sarcoid that gravitates to the nervous system. Peripheral neuropathy does not occur as a feature of MS, a strictly CNS disease, but it is still possible to have peripheral neuropathy along with MS, especially if the patient has been treated with a neurotoxic agent, such as cyclophosphamide.

470. The answer is c. (Victor, pp 1212—1215.) Thiamine deficiency commonly produces a painful sensory neuropathy in persons with alco holism and poor nutrition. This man's history of esophageal varices and acknowledged alcohol abuse makes it highly likely that he has alcoholism-associated thiamine deficiency. Other vitamin deficiencies, including pyridoxine deficiency, are undoubtedly present, but thiamine deficiency is the most likely to evoke a painful neuropathy earliest. Dysesthesias and hyperpathia associated with this neuropathy may be so severe as to make it impossible for the patient to walk or tolerate any type of garment on the feet.

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