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PATIENT 
Mrs. H, a 47-year-old woman, was well until 2 days ago, when she started having low back pain after working in her garden and pulling weeds for several hours. The pain is a constant, dull ache that radiates to her right buttock and hip. Yesterday, after sitting in a movie, the pain began radiating to the back of the right knee. She has taken some acetaminophen and ibuprofen without much relief. Her past medical history is unremarkable, and she takes no medicines. She has no constitutional, bowel, or bladder symptoms.
At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?
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RANKING THE DIFFERENTIAL DIAGNOSIS
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Similar to the patient discussed in the first case, Mrs. H’s low back pain developed after an unusual exertion, and she has no systemic symptoms. However, her pain is worsened by sitting and radiates down the back of her leg (a pain distribution that suggests radicular pain in the L5–S1 distribution, often called sciatica). Both of these pivotal features increase the probability that she has a herniated disk. She has no findings that suggest a systemic cause of her back pain, so the initial differential is limited. Table 7-3 lists the differential diagnosis.
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On physical exam, Mrs. H is clearly uncomfortable. She has no back tenderness and has full range of motion of both hips. When her right leg is raised to about 60 degrees, pain shoots down the leg. When her left leg is raised, she has pain in her lower back. Her strength and sensation are normal, but the right ankle reflex is absent.
Is the clinical information sufficient to make a diagnosis? If not, what other information do you need?
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Mrs. H has sciatica, a positive straight leg raise test, and an absent ankle reflex, a combination that strongly suggests nerve root impingement at L5–S1. One option at this point would be to order an MRI or CT scan to confirm a herniated disk. However, there are 2 questions to consider before ordering a scan:
Will the scan be diagnostic? Remember that a significant percentage of asymptomatic people have herniated disks on CT or MRI.
If the scan is diagnostic, will the finding change the initial management of the patient? Conservative therapy, similar to that for nonspecific back ...