Educational objective: Topical capsaicin causes defunctionalization of afferent pain fibers and depletion of substance P. Initial application results in a burning and stinging sensation, but chronic exposure leads to reduced pain transmission.

A 24-year-old man comes to the physician due to excessive daytime sleepiness. The patient is a college student whose symptoms started around age 12, when he began needing more sleep than his peers to feel refreshed. Two years later, he started having daily episodes of sudden weakness, consistently triggered by laughter or crying, in which his head would nod or his knees would buckle for about 30 seconds. The patient also describes times when he was unable to move for several minutes after awakening from sleep. He mentions nightly dreams that seem very real, often featuring activities that he had been engaged in during the preceding day.

Educational objective: Hypocretin-1 {orexin-A) and hypocretin-2 (orexin-B) are neuropeptides produced in the lateral hypothalamus that promote wakefulness and inhibit REM sleep-related phenomena. Most patients who have narcolepsy with cataplexy have undetectable levels of hypocretin-1 in their cerebrospinal fluid.

A 36-year-old woman is evaluated for several months of tingling and numbness of the right hand and fingers that has progressed to dull, aching pain. The symptoms initially were intermittent but have become persistent, with the pain worsening overnight. The patient works as an office secretary and has had difficulty typing and holding the phone due to hand weakness. On examination, she has weakness of thumb opposition and atrophy of the thenar eminence. The patient attempted treatment with conservative measures but had no significant improvement and has now been referred for surgery.

Educational objective: The carpal tunnel is formed by the carpal bones and the transverse carpal ligament (flexor retinaculum). Carpal tunnel syndrome results from compression of the median nerve as it passes through the carpal tunnel with 9 flexor tendons. Longitudinal incision of the transverse carpal ligament can decrease pressure within the carpal tunnel, improving patients' symptoms.

A 65-year-old man is brought to the emergency department due to acute onset of a severe headache and dizziness. He describes it as a throbbing that localizes to the back of his head, with associated vertigo and mild nausea. The patient has a past medical history of type 2 diabetes mellitus, hypertension, chronic obstructive pulmonary disease, and a recent diagnosis of lung adenocarcinoma. He has smoked 1-2 packs of cigarettes daily for the past 30 years. His temperature is 36. 7 C (98 F), blood pressure is 170/96 mm Hg, pulse is 80/min, and respirations are 14/min. Noncontrast head CT reveals an acute hemorrhage in the cerebellar vermis without mass effect or midline shift.

Educational objective: Acute lesions to the cerebellar vermis typically cause truncal and gait ataxia due to impaired modulation of the medial-descending motor systems. Involvement of the lower vermis and the flocculonodular lobe also causes vertigo/nystagmus due to dysregulation of the vestibular nuclear complex.

A 45-year-old woman is evaluated for numbness and painful tingling of the right hand. The symptoms began 2 months ago and are especially prominent after she plays tennis. On examination, there is diminished sensation in the lateral palm, thenar eminence, and palmar aspect of the first 3Y:z digits of the right hand.

Educational objective: In the forearm, the median nerve courses between the humeral and ulnar heads of the pronator teres muscle and between the flexor digitorum superficialis and flexor digitorum profundus muscles. Compression prior to the takeoff of the palmar branch (eg, between the heads of the pronator teres} results in sensory loss over the lateral palm and palmar aspects of the first 3~ digits.

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A 35-year-old woman, gravida 2 para 1, comes to the office for prenatal evaluation. The patient says she had been using condoms for birth control and unintentionally became pregnant. Her last menstrual period was 2 months ago, and home pregnancy tests are positive. She has not been taking prenatal vitamins. The patient has a healthy, 5-year-old daughter who was born after an uneventful pregnancy. She has a history of rheumatoid arthritis, and her joint symptoms are controlled with methotrexate therapy. The patient has no other medical conditions and takes no other medications. She does not use tobacco, alcohol, or illicit drugs. Vital signs are within normal limits, and physical examination shows no abnormalities. Serum 13-hCG is elevated, and transvaginal ultrasonograehy shows a normal gestational sac and embryo.

Educational objective: Methotrexate and other folic acid antagonists adversely affect rapidly dividing cells (eg, epithelial cells, stem cells, neural tube cells) by limiting the production of precursors essential to DNA synthesis and repair. If used in the first trimester of pregnancy, these drugs can cause major congenital abnormalities (eg, cardiovascular abnormalities, neural tube defects).

A 55-year-old man comes to the office due to intermittent shortness of breath, cough, and chest tightness over the past 3 months. The patient had asthma as a child that improved in adolescence, and he has not required inhalers or steroids since. He feels that his current symptoms are similar to his prior asthma symptoms. The patient was recently diagnosed with essential tremor, which has improved with medical therapy; he has no other chronic medical conditions. He is a lifetime nonsmoker and does not use alcohol or illicit drugs. Blood pressure is 125175 mm Hg, pulse is 58/min, and respirations are 16/min. Physical examination reveals bilateral scattered expiratory wheezes. Heart sounds are normal and there is no extremity edema.

Educational objective: Beta blockers are used in the treatment of essential tremor. Propranolol, a nonselective beta blocker, is the most commonly used therapy and prevents the interaction of epinephrine and norepinephrine with beta-1 and beta-2 receptors to relieve tremor symptoms. However, inhibition of pulmonary beta-2 receptors in patients with underlying reactive airway disease can cause bronchoconstriction, leading to cough, wheeze, and dyspnea.