If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

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A 43-year-old man comes to the emergency department because of a six-hour persistent erection. He complains of some discomfort within the penis, but denies any trauma associated with intercourse. He does have some dysuria. He has never experienced anything similar to this and his facial expression displays his concern. He has no significant medical history, and is not taking any medication, prescribed or illicit.

On physical examination, the corpora cavernosum is rigid and tender, while the glans penis and corpus spongiosum are soft. There is no curvature associated with the erection, and there are no palpable abnormalities along the length of the penile shaft. The testicles are descended and normal to palpation. Rectal examination reveals good sphincter tone and a normal sized, smooth prostate.

Urinalysis and blood counts are all within normal limits. What is the most likely diagnosis?

A. Epididymitis.

B. Hypospadias.

C. Paraphimosis.

D. Penile chordee.

E. Penile fracture.

F. Peyronie's disease.

G. Priapism.

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The correct answer is G.

This patient is suffering from priapism. Priapism is defined as an abnormally prolonged, and usually painful, erection that does not result from sexual desire. It generally involves only the corpora cavernosum and not the corpora spongiosum. The disorder is idiopathic in 60% of the cases, while the remaining 40% of cases are associated with diseases (i.e., leukemia, sickle-cell disease, pelvic tumors, and pelvic infections). The patient usually presents with a history of several hours of painful erection.

As in this patient, the glans penis and corpus spongiosum are soft and uninvolved in the process. The corpora cavernosa are tense with congested blood and tender to palpation. Priapism can be classified as low-flow or high-flow. High-flow is associated with trauma, is non-ischemic, and non-painful. The penis is not fully rigid, and the cause is due to unregulated arterial inflow.

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Low-flow priapism is associated with ischemia, veno-occlusion and stasis of blood, resulting in a painful, rigid erection. There is a build-up of highly viscous, poorly oxygenated blood within the corpora cavernosa. If this persists then interstitial edema and fibrosis of the corpora cavernosa will develop and ultimately lead to impotence.

Choice A: Epididymitis is due to infection and inflammation of the epididymis. The patient complains of heaviness and discomfort in the affected hemi-scrotum.

Choice B: Hypospadias occurs when the urethral meatus opens on the ventral aspect of the penis and not the tip of the glans. It is due to abnormal development in utero.

Choice C: Paraphimosis is a urological emergency. It occurs when the foreskin is retracted and not replaced back into its normal position. The retracted foreskin acts as a tourniquet on the glans, and if it is not reduced, may lead to ischemia of the glans penis.

Choice D: Penile chordee is congenital fibrosis of the tunica albuginea. It leads to curvature of the penis. It is frequently seen in association with hypospadias and may occur on the ventral (more common) or dorsal side of the penis.

Choice E: Penile fracture occurs with traumatic intercourse. A tear in the tunica albuginea, while the penis is erect leads to rapid detumescence with penile edema, pain, and hematoma.

Choice F: Peyronie's disease is defined as an abnormal thickening (or plaque) of the tunica albuginea. It differs from chordee in that it is an acquired condition. It is usually associated with traumatic intercourse. It leads to painful erection, curvature of the penis, and poor erection distal to the involved area. Plaques are palpable, dense, varying in size, and may be located on the dorsal or ventral aspect of the penile shaft.

For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.

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