A 33-year-old woman in her 32nd week of pregnancy (gravida 3, para 2) presented to the emergency department (ED) with a five-day history of weakness and ascending numbness below the right knee. She related a two-week history of right-sided low back pain that radiated to the right buttock and was associated with severe right lower extremity (RLE) pain, most prominent in the posterolateral aspect of the right calf. She denied perianal numbness, incontinence, or other changes in bowel or bladder function. She also denied left lower extremity involvement or trauma.
The patient had had one uneventful pregnancy to date. Her medical history included hypothyroidism, treated with levothyroxine; and anxiety, for which she was taking sertraline. She denied any history of allergies, alcohol consumption, smoking, or illicit drug use. She had been evaluated twice and received reassurance in the two weeks before her presentation to the ED. She was admitted to the obstetric service secondary to pain, and a stat MRI rather than x-ray was ordered by obstetrics. An orthopedic consult was ordered. A spine surgeon happened to be on call.
Examination revealed that the patient walked plantigrade, with her right foot slightly externally rotated. She was unable to dorsiflex or plantarflex her right foot. She was unable to heel- or toe-walk on the right side, possessed 0 out of 5 strength at the right extensor hallucis longus and 2 to 3 out of 5 at the right tibialis anterior and gastroc soleus complex. She complained of pain with right leg elevation exceeding 30° and had very limited sensation to light touch in the right L5 and S1 dermatomes. Deep tendon reflex was absent at the right ankle. The patient refused a rectal exam or post-void evaluation.
The initial diagnosis considered by the ED clinician was sciatica, with a differential diagnosis that included pelvic pain of pregnancy, lumbar sprain strain, sciatica, lumbar disk, herniated nucleus pulposus with radiculopathy, and cauda equina syndrome. Trauma was considered and ruled out, as were malignancies; inflammatory, infectious, or degenerative conditions; or other compressive processes.1
Lumbar MRI demonstrated a very large, right-sided disk herniation at L5-S1 with an extruded fragment that was severely compressing the thecal sac and the right S1 nerve root, causing severe right foraminal stenosis at the level of L5-S1. Degenerative changes were noted at L4-5 with disk dessication and no lesions seen.
The patient was diagnosed with cauda equina syndrome, which was felt to be causing severe RLE weakness and ascending numbness. The options of observation, analgesia, physical therapy, and epidural injections were discussed with the patient; however, surgery was strongly recommended due to her profound weakness and the severity of pain she was experiencing, in addition to the size of the disk herniation. She opted for surgery.
The patient was given epidural anesthesia at the L3-4 level, with a catheter left in place during the procedure. A test dose of lidocaine (1.5 cc) with epinephrine was injected to ensure proper placement, and bupivacaine 0.5% was given in increments of 5.0 cc three times during the case. Propofol was administered for sedation, and a 2.0-mg dose of a long-acting morphine was given to the patient before removal of the epidural catheter. Fetal monitoring was performed by obstetrics throughout the procedure.
A laminotomy, partial facetectomy, and diskectomy were performed at L5-S1 with excision of a free fragment. Surgical pathology described the disk as fibrocartilaginous tissue measuring 3.5 cm x 1.4 cm x 0.6 cm.
Although nearly half of pregnant women experience low back pain, cauda equina syndrome (CES), a complication of lumbar disk herniation, is extremely rare in the gravid patient.2 In a decade-long review of 48,760 consecutive deliveries, LaBan et al3 identified symptomatic lumbar herniated nucleus pulposus in only five patients (approximately one in 10,000 pregnancies). In pregnant women who do experience CES, symptoms most commonly develop between the fifth and seventh month of pregnancy.4 According to Small et al,5 “The major pitfall in diagnosis is not including CES in the back pain differential.”
True CES presents as a triad of symptoms: lower extremity weakness, altered sensation in the skin of the buttocks and upper posterior thighs (saddle anesthesia), and dysfunction or paralysis of the bowel and bladder. However, few patients present with all of the classic symptoms,6 and patients with CES are often dismissed by several clinicians in their search for relief before presenting to a subspecialist. Kostuik et al7 consider “unilateral sciatica with motor and sensory disturbance” a more common presentation of CES; also indicative of this condition, they report, is “urinary dysfunction combined with motor and sensory loss in the presence of a disc lesion.”
The polypeptide relaxin, which is secreted by the corpus luteum to promote joint laxity in late pregnancy, has been associated with low back pain and pelvic pain of pregnancy; it has also been suggested as a possible contributing cause of CES during pregnancy.8,9 Additionally, increased lumbar lordosis with positional and postural stress may cause direct pressure by the gravid uterus on nerve roots. The great vessels may also be compressed by the uterus, resulting in ischemia of the neural element and back pain that radiates to the legs.10 Many cases of lumbar disk prolapse occur during the first and second trimesters. The most clinically incapacitated patients have been found to have the highest levels of relaxin.9
Early diagnosis of CES, through proper physical examination and radiologic studies, is paramount. A rectal examination should be performed to assess for sphincter tone (which may be diminished in 80% of patients) and to assess for perineal sensation.5 Catheterization yielding a postvoid residual urine greater than 100/200 cc is reported to have a specificity and sensitivity of 90% or greater for CES. Small et al5 recommend a straight leg raise maneuver to assess for radiculopathy.
Various studies in the literature support the use of MRI in the gravid patient to confirm the diagnosis of CES and to identify the degree and level of disk protrusion.2-4,11
CES requires urgent surgical decompression.11 Early recognition of CES attributable to lumbar disk prolapse, report O’Laoire et al,12 is essential to prevent irreversible sphincter paralysis. They liken the condition’s urgency to that of extradural hematoma in a head injury.
Disk surgery during pregnancy—preferably a team effort, with obstetrics performing perioperative fetal monitoring—has been deemed a safe management method.2,4 Spinal or general anesthesia during nonobstetric surgery is generally considered safe for both mother and fetus.13,14 Adequate oxygenation without risk for hyperventilation is considered essential.15
In the immediate postoperative period, the patient continued to complain of RLE pain, which abated significantly by the time she was discharged. When she was seen in follow-up four days later, she was able to heel- and toe-walk on the right side, and her strength had improved to 3 or 4 out of 5 at the RLE. She continued to experience diminished sensation to the plantar aspect of the right foot, which persisted at the one-month follow up. At that visit, the patient also reported occasional pain in the right buttock. Physical therapy was started to strengthen the RLE.
By three months postsurgery, the patient had undergone uneventful vaginal delivery. She had an entirely benign exam with 5 out of 5 strength at the RLE and no neurologic deficits. She was cleared to return to light weightlifting with good technique and lumbar support but was told to refrain from running until the sixth month postsurgery.
Although the case patient did not have a “true” (ie, typical) presentation of CES, her symptoms warranted a full workup and treatment to prevent possible long-term sequelae. Medical practitioners should be familiar with the triad presentation of CES. They must differentiate lower back pain of muscular origin from lumbar disk herniation and be able to appreciate the degree of symptom severity reported by the gravid patient. A thorough history and physical assessment must be performed in every such case. When in doubt, the clinician must err on the side of caution, referring the patient for MRI and consulting with a specialist.
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