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.
DISCUSSION
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.”