A 28-year-old woman, gravida 1 para 1, is seen in the clinic a week after spontaneous vaginal delivery. The delivery was performed under epidural analgesia and complicated by a prolonged second stage of labor. Since delivery, the patient has had frequent episodes of fecal incontinence, as well as mild perinea! pain that is relieved by ibuprofen and opioid analgesics. She reports no other medical conditions, and her pregnancy was otherwise uncomplicated. On examination, a healing perinea! laceration shows no signs of infection. Digital anorectal examination reveals decreased anal sphincter tone and loss of the anal wink reflex. Bilateral lower extremity reflexes are 2+ with normal tone.

Educational objective: Pudenda! nerve injury can occur due to excessive stress on the pelvic floor during labor and delivery (eg, prolonged second stage). Nerve injury leads to denervation and weakness of the perinea! musculature (eg, external anal sphincter), which can present as new-onset fecal incontinence.

Electric stimulation of the musculocutaneous nerve causes a rapid twitch of the biceps muscle. Electron microscopy shows numerous vesicles within the musculocutaneous nerve terminals.

Educational Objective: Acetylcholine release from presynaptic terminal vesicles at the neuromuscular junction depends upon the influx of extracellular calcium into the presynaptic terminal. Calcium influx into the nerve terminal occurs following neuronal depolarization and opening of voltage-gated calcium channels.

A 63-year-old man comes to the physician's office due to long-standing osteoarthritis that is refractory to over-the-counter analgesics. After discussing various treatment options with his physician, the patient is referred to a surgeon for right total hip arthroplasty. His acute postoperative course is unremarkable. During a follow-up appointment, the patient reports difficulty walking despite minimal pain. On examination, he leans to his right side when walking. When asked to stand on his right leg, the patient's left hip tilts downward.

Educational objective: Superior gluteal nerve injury results in weakness and paralysis of the gluteus medius, gluteus minimus, and tensor fasciae latae muscles. This causes the pelvis to tilt downward toward the contralateral side (positive Trendelenburg sign). Patients will also lean toward the ipsilateral side when walking to help stabilize the pelvis (gluteus medius gait).

An 82-year-old man is found unresponsive by his neighbor. The patient lives alone in his suburban home. When the neighbor went to check on him, the patient was on the floor and not answering any questions. His medical history is unknown. On arrival of emergency medical services, the patient is obtunded and responds only to painful stimuli. Supportive measures are begun, including endotracheal intubation, but the patient dies en route to the hospital. Autopsy reveals extensive atherosclerotic disease involving the coronary and internal carotid arteries. Histopathologic examination of the brain in the right middle cerebral artery territory shows neurons with intensely eosinophilic cytoplasm and nuclear fragmentation.

Educational objective: Inadequate blood supply to the brain (eg, arterial thrombosis or embolism) leads to ischemic stroke. The first microscopic changes are typically seen 12-24 hours after irreversible ischemic injury and include intense eosinophilic staining of the neuronal cytoplasm (red neurons) and nuclear fragmentation.

A 32-year-old woman describes five episodes of intractable vomiting over the last year. The episodes last several hours and are associated with a sensation that the room is spinning or tilting. At these times, it is difficult for her to walk because she loses her balance. She cannot relate the timing of the episodes to any particular inciting event. Physical examination reveals stability in the Romberg position and during tandem walk. Proprioception is intact.

Educational Objective: Vertigo is a sensation of excessive motion compared to physical reality. It is most commonly due to dysfunction within the vestibular system.

A 27-year-old woman comes to the office due to severe, unilateral, throbbing headaches that occur several times a month. The headaches are associated with photophobia, nausea, and occasional vomiting. Overthe-counter analgesics do not provide significant symptom relief. Her mother has a history of similar headaches. Vital signs are within normal limits. Physical examination reveals no abnormalities. A medication is prescribed to treat her condition and the patient is instructed to take it immediately at the onset of a headache.

Educational objective: The pathogenesis of migraines is complex and multifactorial but includes neurogenic inflammation, vasodilation, and sensitization of trigeminal afferents in the meninges. Triptans are serotonin 5-hydroxytryptamine 18/1 D agonists that stimulate the trigeminovascular serotonin receptors, resulting in inhibition of vasoactive peptide release, intracranial vasoconstriction, and decreased pain. They are used as abortive therapy for acute migraine.

A Caucasian male who suffers from a severe neurological disease dies of an overwhelming respiratory infection. Autopsy shows an atrophic precentral gyrus and thin anterior roots of the spinal cord. Light microscopy reveals a severe loss of neurons in the anterior horn of the spinal cord and in the hypoglossal and ambiguous cranial nerve nuclei; corticospinal tracts stain only faintly, indicating demyelinization.

Educational objective: Amyotrophic lateral sclerosis (ALS) causes both upper and lower motor neuron lesions. Loss of neurons of the anterior horns of the spinal cord (LMN lesion) causes muscle weakness and atrophy. Demyelination of the lateral corticospinal tract (UMN lesion) leads to spasticity and hyperretlexia.