Acute idiopathic ascending polyneuritis, or the Guillain-Barré syndrome, often occurs in the setting of a viral infection and usually begins insidiously. Patients may report weakness, lassitude, or fatigue and are found to have decreased strength primarily in the distal muscle groups. Weakness is typically symmetric and begins in the lower extremities, ascending to involve the upper extremities and most importantly the respiratory muscles. Rarely, the upper extremities may be involved first, and in exceptional circumstances, the facial and extraocular muscles may be involved. Although sensory function is normal and atrophy absent, decreased or absent deep tendon reflexes are commonly noted. Laboratory studies are not particularly helpful (except to exclude some potential diagnoses such as hypokalemia, etc.); however, a small number of patients will exhibit an increased cerebrospinal fluid protein and a moderate lymphocytic or monocytic pleocytosis.

Patients in whom the diagnosis of Guillain-Barré syndrome is suspected should be admitted and closely monitored for changes in vital capacity. Dramatic decreases in pulmonary function resulting in respiratory failure can occur rapidly and without warning. When the vital capacity falls below 10 mL/kg, assisted ventilation is indicated. The use of corticosteroids is controversial; a number of dramatic responses have been reported, and on this basis, a trial of prednisone is often undertaken. Intravenous IgG may be helpful if begun within 14 days of the onset of symptoms, and plasmapheresis may help if begun within 7 days of the onset of symptoms. Urinary retention, wide swings in blood pressure associated with profound diaphoresis, and paroxysmal bradyarrhythmias may be noted with involvement of the autonomic nervous system.

Acute endocarditis runs a fulminant course in which patients become rapidly ill and present with rigors, high fever, and signs of impending vascular collapse. Suggestive physical findings include conjunctival, subungual, oral, or dermal petechiae; Janeway lesions; Osler nodes; retinal hemorrhages, exudates, or Roth spots; splenomegaly; and, in most patients, a heart murmur. Hematuria is noted in more than half of patients. Embolic phenomena are common and include large vessel embolization (cerebral, renal, coronary) and septic pulmonary emboli resulting from right-sided endocarditis. Cerebral emboli may produce seizures, confusion, multiple focal deficits, or hemiplegia.

More invasive bacterial organisms, such as staphylococci, typically produce an acute, fulminant form of endocarditis in which a totally normal endocardial surface may serve as the substrate for initial infection. Patients commonly present with lowgrade fever, malaise, anorexia, weight loss, and generalized weakness; low back pain, headache, and arthralgias are often reported as well.

Subacute endocarditis usually results from infection with less virulent organisms such as Streptococcus viridans and is responsible for presentations that are both varied and subtle. Bacteremia resulting in endocardial infection usually originates from the upper airway, genitourinary tract, gastrointestinal tract, or skin. Subacute endocarditis usually occurs in the context of a previously damaged heart valve or a congenital intracardiac lesion.

The diagnosis of infective endocarditis rests on a high degree of suspicion and the results of blood cultures; specifically, with certain exceptions, persistent bacteremia must be documented. Exceptions include patients treated with antibiotics or those infected with a particularly fastidious organism. Additional laboratory findings include anemia, a mild to moderate leukocytosis, a significantly elevated ESR, a positive latex fixation test, hematuria, proteinuria, circulating immune complexes, and antiteichoic acid antibodies when Staphylococcus aureus is the causative agent. Echocardiography may be useful diagnostically by defining valvular vegetations when these approach at least 2 mm in diameter and in detecting flail valvular leaflets, ruptured chordae tendineae, and regurgitant lesions.

The major complications of infective endocarditis include progressive valvular dysfunction, congestive heart failure (CHF), embolic events, myocardial abscess formation that may extend into the conduction system producing conduction abnormalities, and mycotic aneurysm formation.

Treatment includes 4 to 6 weeks of appropriate intravenous antibiotics, although shorter course regimens are advocated for some patients with certain, specific infections. Because culture results will not be available to the emergency physician, when endocarditis is suspected and there are signs of cardiac failure or systemic emboli, empirical treatment may need to be initiated. If the patient is not in failure or has no signs of embolization, empirical therapy may be delayed until multiple blood cultures have been obtained. The organisms and empirical treatment for infected
native valves differ from those of artificial valves. Native valves are frequently infected with S. viridans, enterococci, S. aureus, Staphylococcus epidermidis and the HACEK group (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella), whereas prosthetic valves are infected by those same organisms plus Gram-negative aerobes. Empirical treatment for infected native valves includes vancomycin 15 mg/kg every 12 hours intravenous plus gentamicin 2 mg/kg loading dose followed by 1 mg/kg every 8 hours intravenous or nafcillin 2 g intravenous every 4 hours plus ampicillin 2 g intravenous every 4 hours plus gentamicin 2 mg/kg loading dose, then 1 mg/kg intravenous every 8 hours. Infected prosthetic valves may be treated with vancomycin 15 mg/kg intravenous every 12 hours (maximum dose of 1 g) plus gentamicin 2 mg/kg intravenous loading dose followed by 1 mg/kg every 8 hours, plus rifampin, 600 mg, orally daily.

Autoantibodies directed against the acetylcholine receptor are believed to be responsible for the clinical expression of myasthenia gravis. The bulbar muscles are predominantly affected; weakness in these muscles produces diplopia, facial weakness, and ptosis as well as difficulty with chewing, speaking, swallowing, and, in the most severe cases, breathing. Patients typically also report marked fatigue.

Particularly when the condition is newly diagnosed, sudden respiratory insufficiency may occur. In these patients, parenteral neostigmine may be given in 1-mg increments over 1 minute up to 3 mg in 1 hour or until an adequate response is obtained. Assisted ventilation may become necessary and should be initiated as needed.

Overtreatment with the cholinergic drugs (such as pyridostigmine) in some patients may precipitate a so-called cholinergic crisis; this is characterized by progressive or worsening weakness and may be difficult to differentiate from a true myasthenic crisis. In these patients, edrophonium, 10 mg intravenous (Tensilon test), may be used diagnostically and therapeutically and will improve muscle strength in patients with myasthenic crisis but will have no significant effect in those with cholinergic crisis. Myasthenia gravis patients with cholinergic crisis should be admitted to the hospital for respiratory care and observation.

Less acutely ill patients are typically treated with pyridostigmine (0.6-1.5 g/day at adequately spaced intervals), thymectomy in patients younger than 60 years of age, and corticosteroids as needed (such as prednisone 50-100 mg daily).