Adolescent disc dysplasia and back pain

Introduction

Back pain with activity (mechanical back pain) is a common source of morbidity in adolescent patients [1–3]. However, pain associated with intervertebral disc degeneration in children and adolescents is usually considered to be a rare and anomalous condition. Despite this, there is an increasing recognition of disc degeneration in adolescent patients marked by disc space narrowing, end plate irregularity, and central hernia of the intervertebral disc through the end plate into the vertebral body. The lesion caused by this disc degeneration is termed a Schmorl's node [4, 5] (see Fig. 1). In earlier studies, the pathology was observed principally in the lower spine, where it is associated with mechanical low back pain; this combination is considered to be a rare entity and was popularly known as lumbar Scheuermann's disease. Recent studies have revealed this pathology to be a painful process that occurs in both the thoracic and lumbar spine without spinal deformity. The symptoms are complex and associated with disc space narrowing, endplate irregularity, and Schmorl's nodes; this condition is now known as adolescent disc dysplasia (ADD). The radiographic characteristics associated with ADD are also seen in juvenile discogenic disease [1, 6–10]. While patients with ADD show evidence of discogenic disc disease, this subset of patients is defined by the presence of pain symptomatology. Although ADD may precede, share genetic components with, and/or encompass similar a pathology to the more familiar Scheuermann's kyphosis, the clinical presentation differs considerably. Scheuermann's kyphosis presents with deformity that is not generally associated with chronic back pain and frequently not associated with pain at all [11, 12]. In contrast, ADD defines a significant back pain syndrome that can become chronic, occurring in either or both the lumbar or thoracic spine and is not associated with spinal deformity. Adolescent disc dysplasia appears to be an appropriate diagnostic term for this troublesome degenerative disc syndrome.

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Fig. 1

Sagittal image of the lumbo-sacral spine. Note the multi-level degenerative disc disease (arrow). Normal sagittal alignment is noted

While the reported prevalence of Scheuermann's disease is 1–3%, some studies document an incidence that approaches 8% [13]. Validated data for ADD specifically are not available, but prevalence figures for disc degeneration vary from 3 to 56%, with studies of patients with an average age of ≤21 years reporting a prevalence of up to 24%. The absence of standardized case definitions of disc degeneration hampers comparisons and interpretations of epidemiologic studies of disc degeneration [14]. Gender distribution is unclear, with some studies describing males being more commonly affected, while others report that both sexes are affected equally [14].

The diagnosis of ADD is typically based on the findings of a clinical examination in conjunction with radiographic findings. Treatment is principally non-operative: a combination of counseling, physical therapy, anti-inflammatory medication, spinal orthosis and, occasionally, surgery. These treatment modalities are similar to those employed in the treatment of various forms of lumbar degenerative disease and are not specific to ADD.

While degenerative disc disease with Schmorl's nodes is a common finding, its role and association with low back pain in adolescents is controversial [10]. Similarly, the natural history, prognosis, and management of this disorder are still poorly understood. Accordingly, we report a contemporary case series of patients afflicted with ADD seen at our tertiary referral center as well as a modern review of the literature on this disease. The purpose of this extended case report is to raise the awareness of this difficult condition, provide familiarity with the natural history of the associated pain and disability and to suggest that ADD should be added to the physician's or surgeon's differential diagnosis for mechanical back pain occurring in adolescence. All patients were evaluated and treated by the senior author (DSD).

Materials and methods

After receiving institutional research board (IRB) approval, we performed a retrospective search through our electronic medical records for patients diagnosed with back pain. A total of 499 such patients were identified for the period 1998–2008. All patients were identified from the senior author's practice (DSD). Inclusion criteria for a diagnosis of ADD included a history of mechanical pain, degenerative disc space changes, and Schmorl's nodes confirmed by radiographs and/or advanced imaging techniques [magnetic resonance imaging (MRI) or computed tomography (CT)]. Exclusion criteria included patients who presented with a pain syndrome that featured principally pain at rest, spinal deformity, such as scoliosis or kyphosis, neurologic symptoms or signs, a history of chronic systemic illness, and all congenital syndromes that involve the musculoskeletal system. Spine pathologies, such as herniated intervertebral disc, spondylolysis or spondylolysthesis, lumbosacral translational vertebra (LSTV), and tumors were also excluded. Clinical information was attained through patient chart review and by examining the radiographic and advanced imaging studies.

Results

Ten patients had the ADD features mentioned above. The data on four patients was insufficient, and these patients were therefore excluded, leaving six patients (four boys, two girls) in this case review. The average age of the patients was 15.2 years. Five patients were Caucasian and one was black. All six patients presented with a chief complaint of mechanical back pain which on presentation had persisted an average of 17 months (range 2–48 months), suggesting a recalcitrant pain syndrome. A history of spine trauma preceding the symptoms occurred in only one of the patients. Five patients actively participated in athletics prior to the onset of the pain, and three patients were sufficiently functionally impaired by the pain to stop all aggressive physical activities, including athletics. Prior to presentation at our center, two patients had undergone either physical therapy or brace treatment without improvement. Five patients described pain only with activity, and one patient was without pain at rest. One patient described principally mechanical back pain but with some pain at rest. Two patients claimed that the pain woke them up from sleep, seemingly from rolling over.

In general, there was a gradual onset of pain, with the pain becoming prolonged and more severe with time. The pain was located primarily in the thoracic spine in two patients and in the lumbar spine in four. None of the patients had a spine deformity (scoliosis or kyphosis). All patients demonstrated increased pain with both forward flexion and extension. On palpation, the tenderness was located over the area of pathology defined by the imaging. One patient had a positive straight leg raise exam. No patient demonstrated increased pain with valsalva maneuver, indicating an absence of intrathecal pathology. Also, neither motor nor sensory deficits were noted in any patient.

Imaging

All patients had plain radiographs as part of the clinical evaluation (Fig. 2a). In four of the six patients, there was evidence of significant endplate irregularity, degenerative changes, and Schmorl's nodes. In two patients, the radiographs were unremarkable, necessitating further evaluation by MRI. Three patients had MRI studies which clearly demonstrated the typical changes of ADD, including Schmorl's nodes (Fig. 2b). MRI appeared to be a more sensitive technique to identify the pathology than plain radiographs, with the degenerative process being much more obvious on the MRI scans than on the radiographs where the same pathology could not be identified (Fig. 2). In another patient, a CT scan demonstrated Schmorl's nodes and disc dysplasia, helping to confirm the diagnosis. As part of an evaluation to determine the cause of the Schmorl's nodes, two patients had dual energy X-ray absorptiometry (DEXA) scans, with neither study revealing evidence of either osteopenia or osteoporosis.

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Fig. 2

Radiograph (a) and magnetic resonance imaging (MRI) study (b) of a patient with adolescent disc dysplasia. Changes consistent with ADD (multi-level degenerative disc disease and Schmorl's nodes) are clearly evident on the MRI scan, while the X-ray only reveals some end-plate irregularity

Discussion

The intervertebral discs are the primary joints of the spinal column. They provide approximately one-third of the height of the vertebral column. The major role of the disc is a mechanical one by constantly transmitting loads arising from body weight and muscle activity through the spinal column [15]. Discs allow the spine to be flexible through flexion, extension, lateral bending, and torsion. The discs also provide the flexibility required for a normal and balanced sagittal plane posture that is needed for spinal health.

The presentation of adolescents with early signs of intervertebral disc degeneration and back pain is not rare and tends to increase steeply with age [15]. Anatomic studies on disc degeneration have noted disk space and endplate narrowing, Schmorl's nodes, a thickened anterior longitudinal ligament, and vertebral body changes. Biochemically, there is a loss of proteoglycan, leading to dehydration of the disc nucleus. In addition, the types and distribution of collagen can be altered. Type II collagen becomes more denatured, and fibronectin content and fragmentation increases—all leading to a degenerative cascade. Based on histology, cell death can be identified by the presence of cells with necrosis and apoptosis. The cause of pain is not clear. Some researchers have postulated that an imbalance in hydrostatic forces under stress loading plays an important role in causing discogenic back pain [15]. The role and significance of the development of Schmorl's nodes in adolescence is not clear. However, the frequent presence of these nodes with ADD suggests that they may be a cause of pain, either directly from a breakdown and/or microfractures of the vertebral endplate or by the inflammatory response associated with these processes. Further, improvement of the pain with time could be explained by healing of the microfractures of the vertebral endplate.

A number of studies have documented the occurrence of disc dysplasia at a young age. Erkintalo et al. [2] found that degenerative changes emerge rapidly after the adolescent growth spurt, observing that by 18 years of age, the frequency of ADD was significantly greater in subjects with low back pain than among the normal control subjects. Individuals with incipient degenerative changes and altered mechanical behavior of the disc may be more susceptible, under everyday loading, to painful minor injuries or strain in ligaments and myofascial tissues [9]. Such early changes can also predict the long-term persistence of back pain and the loss of spine flexibility [16].

The role of trauma as a cause of disc degeneration and back pain in adolescents is controversial. Kerttula et al. [17] and Swischuk et al. [18] proposed that repeated traumatic episodes lead to tears in the annulus fibrosis and cracks in the vertebral endplates. In contrast, other researchers believe that the causative role of trauma is still unclear, with some implicating a failure of nutritional pathways [15] and others describing genetic factors as a possible cause [13, 19–21]. In our study, we noted that only one patient had a history of acute trauma.

Increased accuracy in diagnosing ADD is facilitated through the use of MRI in comparison to standard radiographs. We noted that in instances where radiographs were unable to detect abnormalities in these patients, MRI successfully detected changes consistent with ADD. This result is consistent with those of other studies diagnosing atypical Scheuermann's with non-specific lumbar degeneration [1, 2, 5, 22, 23]. While MRI is the most accurate means of establishing this diagnosis, it does not appear, at this time, to alter the treatment protocol; however, it does serve to “rule out” other diagnoses in patients who present with the symptomatology as described.

There are few outcomes studies for ADD in the literature, and there is no standardized treatment protocol for these patients. In terms of outcomes, Salminen et al. [9] observed the chronicity of this disorder by reporting that 35% of patients continued to have recurrent back pain into adulthood. A prolonged course of pain was evident in most of our patients. Among our patients, the mean duration of pain at presentation was 17 months, and the symptoms persisted despite most of these being treated. In contrast, a study of 58 adolescents with mechanical back pain of all etiologies had a median duration of pain at presentation of 3.57 months [24], while another large study (>13,000 adolescents) found that 86.1% of patients had symptoms for less than 1 month [25]. This is a striking contrast to the typical course of patients with ADD. In a 17-year follow-up study among 20 year old with back pain, Waris et al. [3] noted that disc degeneration was the strongest predictor for a prolonged course and recurrence.

To date treatment protocols are not evidence-based, and most are non-operative and include non-steroidal anti-inflammatory medication (NSAIDS), physical therapy, and lumbosacral brace wear [1]. Our treatment approach was similar, but we found that symptoms were persistent in most patients. Only one patient became asymptomatic, two patients continued to experience intensive pain, two patients had only partial pain relief after prolonged course of physical therapy, and one patient was lost to follow-up. In addition, we did not note any significant benefit from brace treatment. Although we cannot draw a definitive conclusion based on such a small sample size, but similar to the experience of others, only physical therapy appeared to be beneficial for our patients.

Conclusion

Our patient cohort was too small to provide statistically validated data related to ADD. However, based on this review of ADD cases, we recognized clinical signs that can be helpful for understanding this disorder and providing an earlier diagnosis. We summarize these here. 1.

In contrast to other causes of back pain in this age group, with ADD there is a distinct tendency for a prolonged course and a distinct possibility of developing chronic pain. Among our patients, the mean duration of pain at presentation was 17 months.

Adolescent disc dysplasia can be a source of significant morbidity. As it affects multiple segmental levels and creates a course of back pain that is frequently prolonged and can become chronic, it is vital that clinicians become familiar with this disorder and include ADD to their differential diagnosis list for mechanical back pain occurring in older children and adolescents. Hopefully, recognition will allow the treating surgeon/physician to advise the patient and family of the natural history of this disorder and direct them toward the best methods of symptomatic care.