Doctor, Am I Crazy?

Magnetic resonance imaging is the single greatest advancement in the diagnosis of spinal pathology since the introduction of X-rays by Wilhelm Röntgen in 1895.6 MRI provides the clinician with a precise picture of the pathologic anatomy of the spine.2,4,5,7 The technique has been maligned because of its lack of specificity, particularly in patients over 60, where up to a 57% false-positive rate has been reported.1 This should not come as a surprise since we have known for years that the clinical symptoms of acute disc herniation and spinal stenosis can be transient, leaving the patient with a demonstrable pathologic lesion asymptomatic.3 It is up to the clinician, not the radiologist nor the MRI scanner, to decide whether the anatomic lesion discovered by the test is clinically significant.1,8

Over-reliance on the test alone can lead to an erroneous conclusion, a mistaken diagnosis, and an unhappy patient. The following case illustrates this point.

Case Report:

M.D. is a 45-year-old controller for BART who has been disabled for l-l/2 years with a chief complaint of low back pain radiating to the left leg, top of the foot, and great toe. Since l982, the patient has had low back pain effectively managed by chiropractic manipulation. Two years ago, the pain intensified. He was given four caudal steroid injections, medication, hypnosis, TENS units, and acupuncture, and eventually had a two-level microscopic discectomy. The procedure failed to remove all the extruded fragments, and the operation was repeated l0 months later. He felt better for one month, when the pain increased to the point that he had to use a cane because of a slapping sensation he noted with his left foot. The dorsum of his left foot became entirely numb, and he was unable to walk one block, stand for 10 minutes, sit for 20 minutes, or sleep because of left leg pain. He was forced to take four Vicodin tablets per day. An MRI scan was done and revealed "scar tissue enhanced with gadolinium, no evidence for recurrent disc herniation." (fig.1, fig.2)

He was told nothing could be done, and his insurance carrier planned on having him declared permanent and stationary, discontinuing his medical treatment.

Physical Examination:

The physical examination showed tenderness at the L4-5 level. Forward flexion: Hands to thighs. The patient was unable to walk on the heel of his left foot and had decreased sensation to pin on the dorsum of his left foot. The straight leg raising test and bowstring sign on the left produced pain propagating toward the outside of the ankle.

Further testing in the form of pyelogram-histogram-CT scan showed that the material felt to be scar tissue on the gadolinium enhanced MRI was really a sequestered disc fragment responsible for the patient's leg symptoms. (fig. 3)

Removal of the fragment and fusion of the spine was carried out with complete resolution of the leg pain, numbness, and foot drop. (fig. 4, 5, 6)

Discussion:

The MRI is a powerful new tool that creates a precise anatomic image of the spine. This test, like the myelogram and CT scan before it, is not a substitute for a careful history and physical examination. 3,8 The MRI demonstrates the pathologic anatomy. It is up to the clinician to decide whether the abnormality is the cause of the patient's symptoms or not.

Despite two microscopic discectomies that failed to adequately expose and remove the herniated disc over an 18-month period, this patient had unequivocal signs and symptoms of a herniated disc at L4-5. Severe leg pain, which radiates to the outside of the ankle with numbness on the top of the foot and great toe and a foot drop, is highly suggestive of a disc extrusion at L4-5 with L5 root entrapment. The positive straight leg raise and bowstring sign are also suggestive of a mass effect on the dural sac and L5 root, and not of scar tissue (fig. 2). The speckling and enhancement with gadolinium seen on the MRI scan, which theoretically should not occur with an extruded disc fragment, caused the radiologist to make the erroneous diagnosis of scar tissue. In the setting of prior surgery, such reports should be carefully scrutinized by the clinician, who should also review the study firsthand. In this case, scar tissue that grew around the fragment led to the misdiagnosis. The clinical signs and symptoms in this instance led to the myelogram, diskogram, and CT scan. Injection of the L4-5 disc caused severe leg pain, which corresponded to the patient's complaint. A Subsequent CT scan showed the sequestered fragment, which later was confirmed at surgery. (fig. 3, 4)