Thoracic myelopathy due to thoracic spinal stenosis is a rare condition, which is most commonly because of the ossification of the ligamentum flavum (OLF) as first described in 1960 (1). Thoracic spinal stenosis due to OLF has been noted to occur predominantly in older East Asian populations and is rare among whites (2,3). The mean age at presentation is 50 to 60 years, and the duration of symptoms before diagnosis has been shown to range from 1 to 3 years (4,5). Symptoms at presentation are often vague, but generally include chest, abdominal, or lower-extremity motor or sensory changes. Symptoms can include leg numbness, gait disorder, foot weakness, bowel or bladder involvement, zonesthesia of the abdomen or chest, heaviness in the lower extremity, or back pain (6–8).
Although far less common than either cervical or lumbar spinal stenosis, thoracic spinal stenosis deserves consideration in the differential diagnosis of patients presenting with vague lower-extremity motor or sensory symptoms. The inconsistent presentation and spectrum of symptoms can contribute to a delay in diagnosis where initiation of treatment is time sensitive. The case presented illustrates the rare presentation of thoracic spinal stenosis due to OLF in a younger white male.
A 37-year-old white male weightlifter presented to a university sports medicine clinic with a 14-month history of lower extremity symptoms. Onset occurred while running on the treadmill during his workouts and initially involved bilateral anterior thigh paresthesias which lasted several minutes after onset. This occurred intermittently and only with more prolonged activity/exercise. Over the ensuing months, he noted an insidious onset of lower-extremity weakness described as difficulty arising from both a squat and a seated position. He also described three episodes of previous “electrical shock” symptoms radiating from his lower thoracic spine region down his spine (Lhermitte's sign) and into his bilateral lower extremities which lasted for seconds only. He denied the presence of any back pain. Most recently, he had noted left leg dysesthesias which occurred with prolonged walking. Because of this constellation of symptoms, he discontinued his exercise regimen all together. He had been evaluated previously by his primary physician and by neurology without any imaging and had been referred to physical therapy.
Current medical problems included ADHD, and he was currently taking methylphenidate 54-mg extended-release qd. He works in sales in a sedentary position and is married and quit smoking 3 months prior.
Examination demonstrated a fit individual, 6 ft 5 inches and 300 lbs with a BMI of 35.5 kg·m2. His examination was normal other than lower-extremity deep tendon reflexes graded 3+, a strength deficit of 4/5 in left ankle dorsiflexion, five beats of bilateral ankle clonus, and a positive Babinski test on the right only. Given the presence of upper motor neuron signs, a magnetic resonance image (MRI) of the cervical-thoracic-lumbar spine was obtained and initial laboratory work including a normal thyroid stimulating hormone (TSH), folate, and complete blood count (CBC). His vitamin B12 was slightly depressed at 176 pg·mL−1 (normal, 193 to 986 pg·mL−1). His thoracic MRI (Fig.) demonstrated severe canal stenosis at T11-T12 because of a mild disc herniation and OLF with myelopathic changes in the spinal cord. The patient underwent urgent surgical decompression via bilateral T11 to T12 hemilaminectomies with resection of the involved ligamentum flavum. At his 2 wk postoperative visit, he was doing well with clear improvement in his leg symptoms and was returned to work. At his 3-month follow-up, he noted resolution of all lower-extremity symptoms, occasional mild muscle spasms of the lower back, and symmetric strength in the lower extremities including ankle dorsiflexion of 5/5 bilaterally. He was cleared for return to full activity at that time.
Approximately 300,000 to 500,000 persons in the United States have symptoms of spinal stenosis, yet less than 1% of these result from stenosis in the thoracic spine. Thoracic stenosis is most often due to OLF, but also may be caused by ossification of the posterior longitudinal ligament, intervertebral disc herniation, and/or spondylosis. The most common location is in the lower thoracic spine but has been reported throughout the entire thoracic spine. The mean age of patients with thoracic stenosis tends to be older than 50 years but with wide variable age range from the early 20s onward (4,5,7,9).
The etiology of OLF is unclear. It is characterized by heterotopic bone formation in the thoracic portion of the ligamentum flavum. The ossification may be occult in onset or possibly because of some form of trauma to this region of the spine. It is believed that the slow progression of this ossification then leads to impingement of the thoracic spinal cord at the level involved and ultimately can lead to myelopathy, as was the likely case in our patient.
There has been no study of risk factors for thoracic stenosis because of OLF, and this may be because of the low prevalence of the condition. From an epidemiologic standpoint, there are populations in which this condition is more prevalent, such as East Asians and particularly Chinese, Japanese, and Korean populations (2,6). It occurs more commonly among older adults with mean ages of the populations studied ranging from 53 to 62 years (4,5,7). It also has been shown to be more common in men (5,8,9).
OLF as a cause of thoracic stenosis most commonly involves the lower thoracic levels (T10-T12) (4,5,7–9). In general, OLF affects the upper thoracic spine (T1-T4) approximately 25% of the time, the middle thoracic spine (T5-T9) approximately 25% of the time, and T10 to T12 approximately 50% of the time (5,8). It has been described as presenting in one of three patterns; either localized ossification in 11%, discontinuous ossification affecting multiple levels in 53.6%, or continuous ossification affecting multiple sequential vertebral levels in 35.4% (10). Retrospective reviews have demonstrated a significant relationship between thoracic stenosis due to OLF and thoracic myelopathy, such that progression is likely the rule (4,5,9). Furthermore, special consideration needs to be given to the fact that OLF in the thoracic spine also has been associated with clinical disease (stenosis or spondylosis) of either the cervical or lumbar spine as well (4,6,9,11). In a retrospective analysis of 427 cases of thoracic stenosis-associated myelopathy (72.3% due to OLF), 14% of the cases involved coexisting cervical spine disorders and 11% involved coexisting lumbar spine disorders (4). Therefore, in the context of thoracic stenosis due to OLF, imaging of the cervical and lumbar spine is warranted.
A single study has retrospectively evaluated presenting manifestations of thoracic stenosis (7). The most common presenting complaints included lower limb numbness (50% to 70%), subjective lower extremity weakness (27% to 66%), unsteady gait (16% to 41%), lower limb pain (11% to 21%), and low back pain (7% to 8%). Others have described symptoms, such as diffuse numbness and pain in the lower extremities, weakness or heaviness of the legs in ambulation, or pseudo-claudication with or without findings of upper motor neuron signs in the lower extremities (4,6,8,12). Symptom progression was noted in all patients from the time of presentation until definitive management (7). More common physical signs of thoracic stenosis-associated myelopathy include lower-extremity motor deficits (81%), reflex changes (67% to 85%), sensory deficits (64%), ankle clonus (43%), and a positive Babinski test (40%) (4,7). Unfortunately, in this rare condition, there is no predictable pattern of symptoms or signs at presentation, thereby requiring the clinician to include knowledge of this condition as a differential diagnosis is developed.
Delay in the diagnosis of thoracic stenosis is significant. In the Takenaka et al. (7) study, the preoperative mean duration of symptoms for thoracic stenosis due to OLF was 636 d (21.2 months). Interestingly, those with a T11-T12 isolated lesion had the longest mean duration of symptoms of 1063 d (35.4 months) before diagnosis. As in the case presented, when thoracic stenosis involves the lower thoracic levels (T10-T12) the presentation can be more complex and confusing. Clinical manifestations at this level can involve a combination of both upper and lower motor neuron findings. This can lead to confusion as to the level of spinal cord involvement because cervical myelopathy would be more common, and so careful differentiation of the findings is needed. Recall that OLF of the thoracic spine also is associated with stenosis, spondylosis, and myelopathy of either the cervical or lumbar spine as well, so clinicians need to consider these relationships before focused evaluation and/or treatment at a single spinal level. Furthermore, a delay in diagnosis also has been identified as a predictor of poor surgical outcomes (5,8,13).
When thoracic spinal stenosis is considered, an MRI of the thoracic spine is an appropriate first step in imaging. If ossification of either the ligamentum flavum or posterior longitudinal ligament is suspected and not well visualized on the MRI then a focused computed tomography (CT) scan can be obtained at the appropriate thoracic level for better identification of the ossification. Electrodiagnostic testing is of limited utility in evaluating the thoracic spine.
Surgical intervention for symptomatic patients is not standardized and may consist of laminectomy with or without fusion, discectomy, and/or extirpation of posterior involved elements (5,14). Postoperative complications are reported to be in the range of 11% to 36%, and involve dural tears, cerebrospinal fluid leaks, epidural hematoma, postoperative paralysis, and/or wound infections or dehiscence (5,9,14). Studies have examined the predictors of poor surgical outcome and OLF of the midthoracic spine level, longer preoperative duration of symptoms, spinal cord signal change on the preoperative MRI T2-weighted sequences, and increased preoperative severity of the myelopathy all predict poorer surgical outcomes (5,8,13–15).
Thoracic stenosis is the least common cause of spinal stenosis, yet the management of a concomitant myelopathy is associated with a wide array of risks to the patient. Diagnosis should be considered particularly in older East Asian patients with vague abdominal or lower extremity sensory or motor symptoms and/or upper motor neuron signs; however, thoracic stenosis should be considered in any person with such a concerning presentation. MRI is the initial test of choice for evaluating the thoracic spine, and because time to diagnosis is associated with outcomes, earlier diagnosis is relevant.
The author declares no conflict of interest and does not have any financial disclosures.
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