Dr. Tao Le (series editor for the First Aid for the USMLE Step 1) invites you to a free Webinar this Thursday (Nov 1st) from 9-10pm EDT!

This high-yield talk will cover the basics of the USMLE Step 1 including an overview of the boards, goal setting, high-yield topics in each subject area, study strategies, review resources, and study schedules. There will be an opportunity for a live Q & A session at the end of the talk.

The way it works:

1. Register to hold your place now (space is limited).
2. Make sure that your computer meets the system requirements for the visual portion of the online conference (details below).
3. Be able to call the conference phone number to listen to Tao’s presentation. This can be done with a home phone, cell phone, or internet phone.
4. Mark your calendar for November 1st at 9:00pm EDT and come with questions!

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Title: First Aid for the USMLE Step 1 by Dr. Tao LeDate: Thursday, November 1, 2007
Time: 9:00 PM - 10:00 PM EDTSystem Requirements
Required: Windows® 2000, XP Home, XP Pro, 2003 Server, Vista OR
Required: Mac OS® X 10.3.9 (Panther®) or newerReserve your Webinar seat now at:
https://www.gotomeeting.com/register/221875196

Case 8 – A 30-year-old man with double vision

A 30-year-old man presents to the ophthalmology clinic with a complaint of double vision. He states that when he gazes laterally to the right, he sees two images side by side. He does not have this problem when he looks to the left. Past medical history is significant for depression, for which he takes amitriptyline. He denies any ocular pain or recent viral illness. He also denies any history of tick bite and does not smoke cigarettes, drink alcohol, or use intravenous drugs. On physical examination the patient is a well-appearing, well-nourished man. Visual field testing reveals an adduction deficit in the left eye and horizontal nystagmus in the right eye during extreme right lateral gaze. Extreme right lateral gaze also recreates the painless horizontal diplopia that the patient has been experiencing. Conjugate eye movements are observed in all other directions. Accommodation and convergence are normal.

What is the most likely diagnosis?

Internuclear opthalmoplegia (INO). INO results from lesions of the medial longitudinal fasciculus (MLF), a fiber pathway that normally connects the abducens nerve nucleus (cranial nerve VI) located at the pontomedullary junction to the contralateral oculomotor nucleus (cranial nerve III) in the midbrain. Without coordination of these two nuclei, the medial rectus of the adducting eye cannot coordinate with the lateral rectus of the abducting eye. This leads to the characteristic disconjugate lateral gaze that is a hallmark of INO. In addition, the abducting eye also has end-gaze nystagmus. INO can either be unilateral (as in this patient) or bilateral, in which lateral gaze in either direction will produce diplopia.

What other condition should be considered in the differential diagnosis?

INO can easily be confused with a medial rectus palsy since the affected eye appears to have lost its ability to adduct. However, most patients with INO still have the ability to converge, as this ocular movement pattern (bilateral ocular adduction in response to focusing on an object moving closer to the eyes) does not require an intact MLF. Additionally, INO is often the presenting sign of multiple sclerosis (MS). Most (92%) patients who develop INO because of demyelination will progress to full-blown MS. Such patients require close follow-up so that the diagnosis of MS can be made at an early and more easily managed stage. Another important consideration is that myasthenia gravis (MG), which can be life threatening if left untreated, can also initially mimic the findings of INO. Half of patients with MG present initially with extraocular muscle weakness. As such, patients in whom there is any question of the diagnosis should undergo testing for anti-acetylcholine receptor antibody.

What test(s) should be used to determine the etiology of this condition?

The presence of INO suggests that the patient has a brain stem lesion involving the MLF. There are many disease processes that can create such a lesion, including:

1. Brain stem and fourth ventricular tumor
2. Brain stem infarction
3. Drug intoxication (eg, phenothiazines, tricyclic antidepressants, toluene, tacrolimus)
4. Lyme disease
5. Multiple sclerosis (the most common cause of bilateral INO in young adults)
6. Trauma
7. Subdural hematoma
8. Syphilis
9. Viral infection

In this patient, a history of tricyclic antidepressant use may explain his symptoms, as this medication is known to cause INO. Other tests to determine an etiology would include a toxin screen, MRI of the brain, FTA-ABS/VDRL (test for syphilis), Lyme titer, fasting blood glucose, complete blood count with differential, and blood pressure measurement.

What is the most appropriate management for this patient?

Treatment is focused on the etiology of the brain stem lesion associated with INO.

By Daniel Osei, MD, Resident in Orthopedic Surgery, Hospital for Special Surgery; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.

Case 7 – An 18-year-old woman with vaginal discharge and vulvar pain

An 18-year-old woman presents to the health clinic complaining of a fever and malaise. Upon further questioning she also admits to a foul vaginal discharge and vulvar pain. She denies having sexual intercourse recently, but she does admit to “blacking out” at a party 1 week ago and is worried that she may have unknowingly and unwillingly had unprotected sexual intercourse then. Her temperature is 38.6°C (101.5°F). There is significant tender lymphadenopathy in the inguinal region. Examination of the external genitalia reveals three painful, well-demarcated soft ulcers with necrotic bases in the vestibule of the vagina. Pelvic examination reveals a foul-smelling purulent discharge.

What is the most likely diagnosis?

Chancroid. Chancroid is a sexually transmitted infection caused by the gram-negative bacillus Haemophilus ducreyi. The infection is spread by direct sexual contact when the organism comes in contact with an open lesion; the organism cannot invade intact tissue.

How is the diagnosis made?

Chancroid is generally diagnosed clinically as it is difficult to isolate the causative organism, H. ducreyi. The best material for culturing and isolating the organism is aspirated pus from a bubo, but the organism can be isolated in less than a third of cases. Polymerase chain reaction of genital samples is becoming a more widely available form of testing. Importantly, syphilis should be ruled out before making the diagnosis of chancroid.

What other infections should be considered in a patient with genital ulcers?

Patients presenting with genital ulcers should be screened for other sexually transmitted infections such as chlamydia, gonorrhea, HIV, hepatitis B virus, and hepatitis C virus.
Genital ulcers are an important factor in the spread of HIV, as HIV-negative persons with genital ulcers have higher rates of acquisition, and HIV-positive persons with genital ulcers transmit HIV more effectively.

How do the genital lesions in this condition compare to those in other sexually transmitted diseases?

	Granuloma inguinale	Chancroid	Herpes simplex virus (HSV)	Lymphogranu-loma venereum	Syphilis
Causative agent	Calymmatobacterium granulomatis	Haemophilus ducreyi	HSV type 2 (most cases)	Chlamydia trachomatis L1-L3	Treponema pallidum
Appearance/ characteristics of lesions	Granulomatous ulcers with rolled edges	Irregular, deep, well demarcated, nonindurated ulcers	Multiple, small grouped vesicles on erythematous base	Small, shallow rapidly healing ulcers; usually not observed	Indurated, smooth borders on a clean base
Pain	No	Yes	Yes	No	No
Adenopathy	Pseudobuboes	Inguinal; unilateral, painful	Reactive nodes	Matted clusters, often bilateral, painful buboes	Regional, nontender

What is the most appropriate management for this patient?

The best treatment option is one dose of azithromycin (1 g by mouth) or ceftriaxone (250 mg intramuscuarly). Ciprofloxacin (500 mg by mouth twice a day for 3 days) is another option, but less desirable give the multidose requirement.By Cynthia L. Bartus, MD, Resident in Dermatology, Emory University School of Medicine; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.

Case 6 – A 29-year-old pregnant woman seeking nutritional advice

A 29-year-old G2P1 woman presents to her obstetrician’s office at 10 weeks’ gestation for her screening visit. She reports no complaints and states that she has been feeling well. Her past medical history is significant for a seizure disorder that began when she was a teenager. Her seizures have been well controlled with phenytoin, and she was able to discontinue her medication during her previous pregnancy without incident. Since discovering she was pregnant again, she self-discontinued her medication and has been feeling well with no reported seizure activity. She is concerned about maintain an adequate nutritional intake during her current pregnancy.

What is the most important vitamin for this patient to take?

All women of child-bearing age are advised to consume a daily intake of 400 µg of folic acid throughout the periconceptional period to help prevent congenital neural tube defects. This patient’s history of anti-epileptic medication puts her fetus at greater risk for neural tube malformations, and so this patient is advised to ingest at least 4 mg of folic acid daily.

What is the mechanism of action of this vitamin?

Folic acid, a biochemically inactive compound, is the precursor for tetrahydrofolic acid and methyltetrahydrofolate, compounds that are essential for the maintenance of normal erythropoiesis and required cofactors for the synthesis of purine and thymidylate nucleic acids.

What vitamin should be avoided during pregnancy?

Vitamin A, also known as retinoic acid, is frequently used to treat severe cystic acne. Vitamin A should be avoided during pregnancy because of its association with spontaneous abortion and neural tube defects. Although vitamin A is most teratogenic when taken at 5-7 weeks’ gestation, it should be avoided at all gestational ages.

When is iron supplementation required in pregnancy?

Pregnancy causes a physiologic anemia. This is the result of the physiologic increase in plasma volume, which results in an effective decrease in hemoglobin and hematocrit. All pregnant women should take a daily prenatal vitamin that contains iron in order to avoid worsening anemia. Additional iron supplementation at higher doses should be given to any woman with a superimposed cardiac or hematologic condition, such as sickle cell disease.

What vitamin supplements must be given with iron?

When iron is given in large doses, as in the treatment for anemia, copper and zinc should also be prescribed, since large doses of iron inhibit the absorption of these minerals.

By Hindi Stohl Posy, MD, Resident in Obstetrics and Gynecology, Johns Hopkins University; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.

Case 5 – A 35-year-old woman considering abortion

A 35-year-old G3P3 woman presents to the office complaining of breast tenderness, bloating, and mild nausea. Her last menstrual period was 6 weeks ago. She is married and has three children under 5 years of age. She uses oral contraceptive pills for birth control. On physical examination she is afebrile, with a heart rate of 90/min and blood pressure of 140/80 mm Hg. Pelvic examination reveals a normal cervix with a bluish tint. Results of a urine pregnancy test are positive. Transvaginal ultrasound reveals a 6-week-sized gestational sac with detectable fetal heartbeat. The patient is visibly distressed upon hearing about the pregnancy, which she says was unplanned. She says she is overwhelmed with taking care of her three children and does not think she can support another child, financially or emotionally. She says she has considered working with an adoption center, but she was on bed rest for 6 weeks during her last pregnancy and is afraid of the risks and difficulties of carrying this pregnancy to term. She asks for information about abortion.

What types of abortion are available for this patient?

There are two types of abortion available to this patient: medical and surgical. Medical abortion is available for patients with unwanted pregnancies up to 10 weeks’ gestation. Medical abortion uses a combination of mifepristone (formerly known as RU-486) and misoprostol. Mifepristone is a progesterone antagonist administered orally at the provider’s office. Two days later misoprostol, a prostaglandin, is taken orally or vaginally, either at the provider’s office or at home. Most patients will pass the products of conception at home in the next 4-24 hours.

Surgical abortion is available until 22-24 weeks’ gestation (depending on state law), with procedures available in the third trimester to protect the life or health of the mother. The most common surgical abortion procedure is the vacuum aspiration, also called the dilation and suction curettage (D&C). The cervix is dilated and the uterine contents are evacuated with electric suction. Up to 10 weeks’ gestation, a hand-held syringe can be used instead of the electric suction in a procedure called manual vacuum aspiration.

What is the epidemiology of abortion?

Half of all pregnancies every year in America are unplanned, and half of those end in abortion. If current rates continue, 35% of American women will have had an abortion by the time they are 45 years old. Eight-eight percent of abortions are performed in the first trimester, while only 2% are done after 21 weeks’ gestation. Fifty percent of women having an abortion report that they were using birth control at the time of conception.

What are the complications of abortion?

Legal abortion is a very safe procedure with a complication rate of <1%. The most common complications of medical abortion are incomplete abortion or prolonged bleeding, both of which are treated with a suction procedure. The passage of the uterine contents is often uncomfortable, with heavy cramping similar to that experienced during a spontaneous miscarriage. Complications of surgical abortions are rare, but include perforation, infection, and reactions to anesthesia. There is no evidence linking abortion and increased breast cancer risk.

What is the recommended follow-up after an abortion?

Medical abortion requires a follow-up visit 7-14 days after administration of the mifepristone to ensure that the abortion was completed. Surgical abortion follow-up is usually 2-3 weeks after the procedure. Contraception counseling should be started on the day of the procedure and continued at the follow-up visit.

By Melissa Rosenstein, MD, Resident in Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco Medical Center; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.

Case 4 – An 18-year-old woman after a motor vehicle accident

An 18-year-old woman is brought to the emergency department by ambulance after suffering a motor vehicle accident. The patient had been alert when the paramedics arrived at the scene of the accident, but her level of consciousness declined en route to the hospital. The patient told the paramedics she had been unrestrained and had hit her windshield during the collision. On presentation the patient appears drowsy but is responsive to verbal commands. She complains of back and neck pain and a headache. The patient has a contusion and abrasion over her right temporal region; the remainder of her head, ear, eye, nose, and throat examination is normal. Neurological examination reveals no focal deficits, and cranial nerves II-XII are intact. Vital signs, a complete blood count, and blood chemistry test results are within normal limits. A lateral x-ray of the cervical spine reveals no abnormalities. Noncontrast CT scan of the head shows a small fracture of the skull in the temporal region and an underlying extra-axial lenticular hyperdensity.

What is the most likely diagnosis?

Epidural hematoma (EDH). EDH is an accumulation of blood between the inner table of the skull and the dural membrane. In a patient with a history of blunt head trauma, radiographic evidence of a temporal bone fracture, and an underlying lens-shaped collection of blood, EDH is the most likely diagnosis. Because the underlying brain has usually been spared from injury, prognosis is excellent if treated quickly and aggressively.

What are the typical clinical findings associated with this condition?

EDH is sometimes (approximately 20% of cases) characterized by a patient experiencing a lucid interval prior to experiencing a decline in consciousness. Many patients are comatose by the time they receive medical attention. Other common presenting signs and symptoms include headache, seizure, and vomiting.

What other symptoms can occur with this condition?

As in all expanding space-occupying lesions, increasing intracranial pressure can lead to brain herniation and possible death. Signs of increasing intracranial pressure that may signal imminent herniation include:

1. A triad of bradycardia, respiratory depression, and hypertension (Cushing’s triad)
2. Cranial nerve VI palsy
3. Dilated, sluggish, or fixed pupils
4. Papilledema secondary to impaired axonal transport and congestion of the optic nerve
5. Spontaneous periorbital bruising

What risk factors are associated with a worse prognosis?

The mortality rate for EDH is 5%-40% depending on the presence of the following risk factors:

1. Advanced age
2. Increased hematoma volume
3. Increased intracranial pressure
4. Intradural lesions
5. Lower Glasgow Coma Scale rating
6. Papillary abnormalities
7. Rapid clinical progression
8. Temporal location

What is the most appropriate management for this patient?

Treatment for EDH is the same as for all head trauma. Initial management focuses on hemodynamic stabilization and management of life-threatening issues. Burr holes are indicated if brain herniation appears imminent and definitive surgery cannot take place in the emergent setting. Definitive surgical treatment involves craniotomy and excavation of the underlying hematoma.

By Daniel Osei, MD, Resident in Orthopedic Surgery, Hospital for Special Surgery; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.