Motor Weakness after Caudal Epidural Injection Using the Air-acceptance Test
The patient, a 44-year-old female with a weight of 48 kg, height of 158 cm, and no significant medical history or underlying condition was admitted to the orthopedic ward for low back pain. Despite admission and conservative treatment, her pain failed to subside and she was referred to our pain clinic. However, she had no symptoms of radiculopathy of the lower extremities. Vital signs upon admission were within the normal range, with a blood pressure of 110/70 mmHg, a heart rate of 74 beats per minute, and oxygen saturation of 98%. Chest X-ray, electrocardiogram, complete blood cell count, blood chemistry, prothrombin time, activated partial thromboplastin time, and other laboratory findings revealed no abnormalities. Nevertheless, the patient could not walk straight for 200 meters due to her low back pain. A physical examination showed a local tenderness around the L4, L5, and S1 vertebrae, but the straight leg raising (SLR) test showed negative results. Motor and sensory functions were fully intact, and defecation and urination were normal, as well. L-spine magnetic resonance imaging (MRI) showed mild bulging of the intervertebral discs from L3 through L5.\nTo relieve her symptoms, she received a caudal epidural injection. Local anesthesia was given around the puncture site with 3 ml of 2% lidocaine. Then, a 20-gauge spinal needle was inserted 2 cm inwards, and 1 ml of air was injected which checking for any bulging or crepitus of the tissues overlying the sacrum or over-resistance of the plunger. Resistance was present; thus, the needle was advanced 0.5 cm farther. Then, 1 ml of air was re-injected, and the loss of resistance was confirmed. No blood was aspired, confirming negative vessel puncture. In total, 2 ml of air were used during the procedure. After correctly positioning the needle, 15 ml of 0.3% mepivacaine and 20 mg of triamcinolone were injected.\nTen minutes later, the patient felt numbness in both legs and muscle weakness in the right lower leg. Decreased motor and sensory function failed to resolve spontaneously in the right lower leg and continued to persist for 1 hour. Specifically, sensory function, which was checked at the posterolateral side of the right lower leg and the plantar area of the right foot, decreased to just 20/100 compared to the corresponding areas of the normal left leg. With regard to decreased muscle strength, flexion and extension of the right knee was normal, but at the right ankle, dorsiflexion was marked as motor grade IV and plantar flexion as motor grade I. Vital signs were within the normal range, with a blood pressure of 120/80 mmHg, a heart rate of 78 beats per minute, and oxygen saturation of 98%. Close observation was done for the next 4 hours, but the symptom persisted, making the patient anxious. To rule out the possibility of a hematoma caused by vessel injury, the patient underwent an MRI, which showed adjacent to the right S1 nerve root a 13-mm-long air bubble with a low signal intensity in both the T1- () and T2- () weighted images. A consultation with doctors from orthopedics and radiology was carried out, and based on the distribution of symptoms, the cause was agreed to be a space occupying lesion, probably an air bubble, near the right S1 root. The patient was put on close observation, and symptoms began improving spontaneously 7 hours post-procedure, with muscle strength reaching motor grade III for plantar flexion. Sensory function also improved to 40/100. After 24 hours post-procedure, the patient had almost completely recovered, with a motor grade of IV and sensory function of 80/100. Forty-eight hours after the initial procedure, motor and sensory functions were fully back to normal.