A Rare Cause of Cauda Equina Syndrome

Abstract

Introduction Low back pain with radicular symptoms into the feet is a common complaint among patients in the orthopedic office. Some spectrum of disease in the intervertebral discs or neural foramen is usually the culprit. The typical therapeutic course includes anti-inflammatory medications, physical therapy for core strengthening, epidural spinal injections, or ultimately surgical decompression. Occasionally this is not the case, as is discussed below. History The patient, a 45-year-old black woman, presented to the orthopedic office with the chief complaint of 3 months of escalating low back pain described as an electric pain that radiated down to her right fifth toe. She denied any weakness or loss of sensation in her lower extremity, as well as bowel or bladder incontinence. Her past medical history was significant for obesity. She did not have any known endocrine disorders. Physical Examination and Imaging Her initial examination was notable for tenderness of the right paraspinal lumbar region with palpable muscle spasm and a positive straight leg raise test result at 30° of hip flexion. Her roentgenograms revealed anterior osteophytes on the L4 and L5 vertebral bodies as well as foraminal narrowing at the L5-S1 nerve root. Working Diagnosis and Care Plan The patient was diagnosed with lumbar radiculopathy. She was prescribed core strengthening and nonsteroidal anti-inflammatory medications. Approximately 2 weeks later she began experiencing urinary incontinence and was found to have diminished light touch sensation in the S1 distribution. MRI revealed severe L4-L5 and L5-S1 disc extrusion that effectively obliterated the central canal and caused biforaminal stenosis in addition to mass effect on the L5 and S1 nerve roots (Figs. 1 and 2).Figure 2: Mild bulging disc, no canal stenosis.Figure 1: Reported as a large herniated disk with total canal obliteration. At surgery found to be an ossified posterior longitudinal ligament adhered to the epidurum.The patient was immediately taken to the operating room for decompression. Surprisingly, the orthopedic surgeon encountered bone and adherent dura where he expected to find extruded disc. After review with the radiologist and confirmation with a CT myelogram it was established that there was ossification of the lumbar posterior longitudinal ligament. Discussion Ossification of the posterior longitudinal ligament (OPLL) is a pathologic ectopic ossification that most commonly occurs in the cervical and thoracic spine with a male to female ratio of 2:1. OPLL has been most extensively studied in the Asian and more specifically the Japanese populations, but has been receiving increased recognition in other populations. This disease appears to have a multifactorial etiology in which genetic and environmental components play a role [1,2]. Lumbar involvement appears to be a rarity and is more often found in individuals older than 40 years [3]. Most individuals with OPLL in any segment of the spine are asymptomatic, but those that do progress cause a myeloradiculopathy due to spinal cord and nerve root compression. The posterior longitudinal ligament traverses from the second cervical vertebrae to the sacrum along the posterior surface of the vertebrae and discs. The annulus fibrosus of the intervertebral discs blends with the deep layer of the posterior longitudinal ligament. Unlike the close association with the intervertebral discs, there is connective tissue and venous plexus between the ligament and the vertebral body. The superficial layer of the ligament is where the ossification is initially seen; it is composed of lamellar bone and calcified cartilage. The ossification expands in thickness and in width beyond its anatomic borders. In the lumbar spine the posterior longitudinal ligament is wider at L1 and progressively becomes less broad toward the sacrum. Therefore, most lumbar disease from OPLL is seen at the upper lumbar levels. Furthermore, there is much more space in the lumbar spinal canal, which allows for much more progression of ossification without symptoms. In the past 15 to 20 years, there has been more research into the biology of this disease due to advancements in genetic technology. Through pedigree and twin studies researchers began to discover the possibility of the existence of genetic factors in OPLL [1]. Studies from 1996 and 2003 found polymorphisms of collagen genes on chromosome 6 and 21, respectively, were associated with a higher incidence of disease [4–6]. Mouse studies uncovered a possible link with the nucleotide pyrophosphate gene. This gene was mapped to human chromosome 6. Several studies noted specific intron deletions in patients with OPLL but these results have not been reproducible [7]. Further research is warranted, as causal relationships cannot be clearly defined. Various growth factors and cytokines have also been studied through histochemical and cytochemical means. The most widely studied are bone morphogenic proteins and transforming growth factor-γ [8]. Other theories include mechanical stress, which leads to a biochemical response, and imbalance between bone resorption and synthesis, resulting in high serum concentrations of certain proteins or cytokines involved in bone synthesis [9]. The epidemiologic data on OPLL, as stated before, focus on OPLL of the cervical and thoracic spine. In Japan, the prevalence among those 30 years of age and older is 1.9% to 4.3% [8]. Prevalence data collected in Korea and Taiwan were similar to data found in Japan. OPLL is becoming more recognized and diagnosed in North America. Nevertheless, the current data suggest a prevalence of 0.12% [8]. Although most of the North American cases were considered to be sporadic several familial cases were reported. Associated risk factors for OPLL include non–insulin- dependent diabetes mellitus, hypoparathyroidism, hypophosphatemic rickets, and adult-onset obesity. Specifically, there has been research into the connection between elevated insulin levels and OPLL [10]. Specific dietary lifestyles, such as high salt and protein intake, have been linked to OPLL in Japan and Taiwan. Sleeping more than 9 hours and less than 5 hours may also be a risk factor for OPLL [8]. Associated diseases include diffuse idiopathic skeletal hyperostosis, ossification of the ligamentum flavum (or yellow ligament), and hypertrophy of the posterior longitudinal ligament. The coexistence of these diseases with OPLL is rather common. The natural history of this disease is to encroach on the spinal cord and the foramen and cause myelopathy. Longitudinal studies of asymptomatic individuals who were diagnosed with OPLL revealed approximately 70% remain asymptomatic for 10 to 20 years [11]. Therefore, prophylactic surgery is not advocated. Alternatively, approximately 60% of those individuals that presented with symptoms at the time of diagnosis experienced worsening myelopathy. The disease can progress both axially and longitudinally over time. Imaging for OPLL includes roentgenograms, MRI, and CT scan. Evidence can be seen on plain film, but is much better visualized on CT scan with bone windows. In fact, CT scan is the imaging modality of choice [3]. Sagittal reconstruction on CT scan is very helpful in delineating the extent of disease. Often there is a distinct radiolucent line between the vertebral body and the OPLL, which represents the connective tissue, venous plexus, and the deep layer of the ligament. MRI can be deceiving, as noted in this case, for herniated nucleus pulposus. Once symptomatic, surgery is the preferred treatment for those with weakness, intractable pain, or bowel or bladder incontinence. The patient can undergo laminoplasty or fusion. Laminoplasty has the benefit of not endangering the vertebral artery or causing a cerebrospinal fluid leak. Unfortunately, the decompressive effect is nonexistent and there are some reports that this procedure could further progress ossification [9]. Although there may be progressive ossification many subjects do not have new or progressive symptoms. Nevertheless, laminoplasty is not currently the preferred method. Fusion, however, has the ability to eliminate segmental motion. The posterior approach that is often used in the United States for decompression of herniated discs is not recommended in OPLL. Instead, an anterior floating method with an autograft fusion appears to slow or decrease the frequency of disease progression [8]. In this approach, in order to minimize risk of cerebrospinal fluid leakage, a thin layer of OPLL is left adherent to the dura. A combination anterior-posterior approach has been advocated for lesions that occupy a large part of the spinal canal [5]. Conclusions In summary, lumbar OPLL is a much less characterized disease than its counterpart in the cervical and thoracic spine. One can theorize that the genetic and environmental factors would be similar for OPLL, but due to the low prevalence of disease less is known. CT scan with sagittal reconstruction is preferred when OPLL is suspected and an anterior surgical approach is recommended unless a large portion of the spinal canal is involved. This case of a black woman with L4, L5, and S1 involvement is clearly unique.