Clinical Case: Leg Pain (Part 1)

Here is another in my occasional series (ok, it's only the second) designed to illustrate specific teaching points in Primary Care. As before, this is most definitely NOT the typical case presentation of some bizarre diagnosis intended to show off how smart I am. In fact, my intent is to highlight an error in my thought process with the hope that others might learn and avoid the same pitfall in their own clinical practices. (Unless I was just really stupid and no one else would ever make the same kind of mistake I did.) I have received the patient's full and explicit permission to post this case.

A 60-year-old white female smoker came to my office complaining of right leg pain for five years. it was described as a tightness in the front of the thigh that came on after walking five blocks or less. When she stopped to rest, the pain abated promptly within one minute. Over time she had noticed it gradually increasing in severity. There was no complaint of any pain or discomfort in the left thigh, either lower leg or foot. She was taking Lipitor for an elevated LDL (224 in 1997; on statins since then.) She was on no other medications and had no other medical problems.

On examination, her blood pressure and BMI were within normal limits. The right leg was unremarkable. There was no swelling, tenderness, deformity or asymmetry of color or temperature. I thought her right pedal pulses were somewhat diminished compared to those in the left foot. The rest of her general physical examination was completely normal.

My diagnosis was claudication; pain caused by a blockage in the flow of blood to the right leg that only produced pain when extra blood flow was needed -- as with walking. As soon as she stopped and the muscle's need for extra blood flow decreased, the pain went away. Although the classic location for intermittent claudication is the calf, I felt the patient's description and timing of the pain -- along with her status as a smoker -- made it the most likely diagnosis.

The simplest, cheapest and least invasive test to document problems with blood flow to the legs is pulse volume recordings performed with doppler ultrasound. Here was the report:

Normal amplitude of the arterial curve, a normal contour of the curve and a normal systolic pressure with an [ankle brachial index] of 1.0 on the right and 0.98 on the left. This study is essentially normal, with no evidence of vascular occlusive disease involving either lower extremity.

With a report showing normal blood flow to both legs, I began thinking about other causes of leg pain with exercise that abates with rest. There's something called spinal stenosis, a narrowing of the spinal canal that exerts pressure on the spinal cord with an upright posture. Bending forward relieves the pressure and the pain. I called the patient and asked again about how her pain was relieved; does she typically bend over when she takes a rest from walking? She wasn't sure; she thought she usually sat down. It was easy to visualize someone hunching over while seated, so I thought, "Close enough." I got an MRI of her lumbar spine which showed focal right-sided paracentral disk protrusion at T12L1, but no stenosis or cord compression. The patient then requested an x-ray of her right hip, thinking the pain might be from arthritis. The films were normal.

Next, she saw an orthopedic surgeon who felt the MRI abnormalities had nothing to do with the pain. He felt it was neurogenic, started her on Lyrica and referred her to a neurologist.

The neurologist ordered another study which confirmed the correct diagnosis.

Post guesses in the comments. I expect that many, if not most, will be correct. I'll put the answer up in a few days. Remember, this is not an exercise in diagnostic obscurity. It is an example of an erroneous thought process interfering with a simple diagnosis.