A 48-YEAR-OLD MALE, furniture mover by occupation, complained of severe low-back pain. For three days prior to presentation, he stayed in bed. His clinician ordered a non-contrast MRI of the lumbar spine. Following his MRI, an ESR, CRP and CBC were obtained and were within normal limits.
Magnetic resonance imaging (MRI) of the lumbar spine is frequently employed to evaluate complicated cases of low-back pain and/or radiculopathy subsequent to a non-specific evaluation by radiography. The increased sensitivity and specificity of MR imaging often narrows the patient’s differential diagnosis and may serve to exclude uncommon threatening disorders, such as malignant neoplasm or infection.
A common finding at MR imaging of the lumbar spine is abnormal signal intensity within the vertebral body, disc and endplates, particularly at L4-L5 and L5-S1. These body, disc and endplate changes are reflective of intervertebral disc degeneration and are an age-associated source of discogenic pain. Modicet al.1 classified these changes into three groups (I-III) utilizing histological and MR imaging correlation; mixed subtypes have also been described.
The Modic Type 1 change is revealed as low signal on T1-weighted and high signal intensity on T2-weighted images in the body and endplate. The Type 1 Modic changes are pathologically associated with fissuring of the cartilaginous layer of the vertebral endplates and by increased vascularity localized within the adjacent subchondral vertebral body. The inflammatory process underlying Modic Type 1 has been the subject of considerable debate with proposed etiologies ranging from repetitive trauma to the disc, pro-inflammatory cytokines and segmental lumbar instability.2-4 Recently, the debate has focused on the detection of bacteria isolated from patients with disc herniation and low-back pain. Ganko et al. in a recent systematic review leaves the question open as to whether degenerative disc disease has a microbial etiology.5
Type 2 Modic change is characterized by fatty infiltration along the vertebral endplates although some bone marrow edema may also be seen. Hyperintense signal on T1-weighted and hyperintense or isointense signal intensity are noted on T2-weighted MR images. Type III Modic changes display reduced endplate signal intensity on both T1- and T2-weighted images. This finding is the equivalent of vertebral endplate sclerosis identified at radiography. It may reflect bone mineralization and not actually vertebral marrow change.6
The differential diagnosis for Modic Type 1 changes on lumbar MR imaging is unfortunately inclusive of threatening infiltrative marrow lesions, such as metastatic carcinoma, multiple myeloma and spondylodiscitis (infection of vertebral body and disc), among other diseases. Since these disorders also provoke severe and progressive low-back pain and their MR imaging marrow changes may be identical to Modic Type 1 (low signal on T1 and hyperintensity on T2), suspicion of the presence of these disorders often requires additional investigation.
Intervertebral disc space infections (spondylodiscitis) typically give rise to vertebral bone marrow edema, with low signal intensity on T1 and high signal intensity on T2, which crosses the disc space from one vertebral body to the next. This appearance may also mimic Type 1 Modic change. The intravenous administration of an MR gadolinium contrast agent, unfortunately, does not provide reliable radiologic differentiation as contrast enhancement of the intervertebral disc, and the vertebral endplates may occur in both spondylodiscitis and Modic Type 1. The presence of desiccation is common in degenerative discs and will usually present a normal or hypointense T2 signal while the T2 signal intensity is often increased in the setting of spondylodiscitis. The vertebral endplates are often irregular but still preserved in degenerative disc disease. Erosive or destructive endplate findings are suggestive of spondylodiscitis or another infiltrative marrow disorder. In addition, the presence of a paraspinal mass or epidural fluid collection indicates high specificity for spondylodiscitis or a neoplastic process.
Newer Generation MRI Technology
The evolution of newer generations of MRI technology (e.g., ultrahigh fields, echoplanar imaging, high performance gradients, dedicated coils and novel pulse sequences) have dramatically increased imaging capabilities. Diffusion-weighted MR imaging (DWI) is currently employed in the investigation of intracranial disorders, including ischemia, infection and tumors of the brain. The DWI sequences display the restricted molecular diffusion of tissue water molecules, an extremely sensitive measure of underlying pathology. However, the use of DWI in the evaluation of the musculoskeletal system and bone marrow disease, in particular, is only recently emerging. Diffusion-weighted imaging proved to be the most successful MR sequence for predicting the final clinical diagnosis of Modic Type 1 disc degeneration versus infection.7
Laboratory examinations such as acute phase reactants, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are widely available, and when abnormally elevated, suggest the presence of pathological tissue injury. An abnormal complete blood count (CBC) may identify anemia, leukocytosis or platelet deficiency (thrombocytopenia) findings that reinforce the probability of an invasive marrow disorder, such as spondylodiscitis, or a malignant process.
The differential diagnosis for Modic Type 1 as seen in the patient presented requires cautious consideration of the patient’s clinical and laboratory status, in conjunction with radiological expertise to increase the probability of the appropriate diagnosis and ensure optimal clinical outcomes.
1) Modic MT, Steinberg PM, Ross JS, et al. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193–99.
2) Crock HV. Internal disc disruption: a challenge to disc prolapse fifty years on. Spine. 1986;11:650–53.
3) Ohtori S, Inoue G, Ito T, et al. Tumor necrosis factor-immunoreactive cells and PGP 9.5-immunoreactive nerve fibers in vertebral endplates of patients with discogenic low back pain and Modic type 1 or type 2 changes on MRI. Spine. 2006;31:1026-31.
4) Toyone T, Takahashi K, Kitahara H, et al. Vertebral bonemarrow changes in degenerative lumbar disc disease: an MRI study of 74 patients with low back pain. J Bone Joint Surg Br. 1994;76:757–64.
5) Ganko R, Rao PJ, Phan K, Mobbs RJ. Can bacterial infection by low virulent organisms be a plausible cause for symptomatic disc degeneration? A systematic review. Spine (Phila Pa 1976). 2015 May 15; 40 (10):E587-92.
6) Xu L, Chu B, Feng Y, Xu F, Zou YF. Modic changes in lumbar spine: prevalence and distribution patterns of end plate oedema and end plate sclerosis. Br J Radiol. 2016 Feb 15:20150650.
7) Patel KB, Poplawski MM, Pawha PS, Naidich TP, Tanenbaum LN. Diffusion-weighted MRI ‘claw sign’ improves differentiation of infectious from degenerative Modic type 1 signal changes of the spine. Am J Neuroradiol. 2014 Aug;35(8):1647-52.