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Acute Schmorl’s node: a forgotten cause of severe back pain

A Schmorl’s node (SN) refers to an intervertebral disc herniating into the vertebral body. Its incidence in the general population has been estimated between 10% and 16% (1). The majority of SNs develop chronically in asymptomatic people and are detected incidentally. A small minority of patients develop acute SN and experience severe pain (2). We report two cases with acute back pain found to have an SN on imaging. A 57-year-old postmenopausal woman with a history of hypermobility and chronic low back pain secondary to facet joint arthritis presented with an acute flare of pain. The pain had worsened over the past couple of weeks, and was right sided with referral to the posterior right thigh. There was no bowel, bladder, or sensory disturbance. Pain was aggravated by bending backwards. A straight leg raise test was normal, with no abnormal neurological signs. Tenderness was found over the interspinous ligaments at the level of L3/4 and L4/5 vertebrae in the prone position. Magnetic resonance imaging (MRI) of the lumbosacral spine showed an interval development of superior endplate infraction with an SN in the L1 vertebral body, and surrounding marrow oedema (Figure 1A). This was a new development in comparison to an MRI scan in 2013 (Figure 1B). A dual-energy X-ray absorptiometry (DEXA) scan performed in October 2014 had shown borderline osteopenia in the lumbar spine and total hip region. She was treated with analgesia and physiotherapy and her symptoms settled within 4 weeks. A 52-year-old postmenopausal woman with chronic low back pain presented with sudden onset of severe mid-thoracic pain while riding her pony. There was no history of trauma. A straight leg raise was normal bilaterally and there were no abnormal neurological signs. Rotation of the thoracic spine was bilaterally painful and tenderness was evident over T3–T9 thoracic spine. MRI of the spine confirmed a mild wedge compression fracture involving the superior endplate of T9 with associated SN, marrow oedema, and fatty marrow change. Several further SNs were seen within the lower thoracic spine with no associated oedematous marrow change (Figure 1C). DEXA imaging confirmed osteopenia (T score −2.3 in lumbar spine). She was treated symptomatically with analgesia and physiotherapy, and showed good recovery. Several mechanisms of pathogenesis have been proposed for the development of SNs. These include degenerative, developmental, traumatic, and pathogenic mechanisms. Ageing degenerates the cartilaginous endplate, birth defects can cause ossification gaps and notochord extrusion defects, and trauma disrupts the physical barriers holding the disc and vertebrae in place (3). Despite these various proposed mechanisms, the aetiology of SNs remains unknown. The thoracolumbar spine is the most common site for the development of SNs (4). This correlates with maximum axial loading (5) at this anatomical location increasing the chances of a disc herniation. The history of sudden-onset severe pain may raise concerns of an insufficiency osteoporotic fracture. National Institute for Health and Care Excellence (NICE) guidance for the management of back pain suggests that MRI is not appropriate in simple non-specific back pain. However, it can be helpful to differentiate SN from an osteoporotic fracture, if this was considered. History and clinical examination should be accompanied by high-quality MRI in a patient presenting with back pain warranting further assessment (6). Plain radiographs are not sensitive enough to detect SNs found on MRI, especially if they present acutely. This is partly because X-rays can only detect larger lesions with a recognizable reactive process in the vertebrae (7). MRI can reliably detect increased vascularization and free water content reflecting inflammation and marrow oedema (8), and enable differentiation from an osteoporotic fracture. Acute painful SNs often respond to painkillers, bed rest, or bracing. Improvement is seen over a few months, with settling marrow oedema and resolving inflammatory reactions. Nerve blocks or vertebroplasty have been helpful in those with persistent disabling pain despite conservative management (9). In conclusion, SNs should be considered in a patient presenting with acute back pain. MRI scanning will help to differentiate an SN from a suspected osteoporotic fracture. Scand J Rheumatol 2018;47:429–430 429