Modic changes, possible causes and relation to low back pain
From: Med Hypotheses. 2008;70(2):361-8. Epub 2007 Jul 10
In patients with low back pain it is only possible to diagnose a small proportion, (approximately 20%), on a pathoanatomical basis. Therefore, the identification of relevant low back pain subgroups, preferably on a pathoanatomical basis, is strongly needed. Signal changes on MRI in the vertebral body marrow adjacent to the end plates also known as Modic changes are common in patients with low back pain (18-58%) and is strongly associated with low back pain. In asymptomatic persons the prevalence is 12-13%. Modic changes are divided into three different types. Type 1 consists of fibro vascular tissue, type 2 is yellow fat, and type 3 is sclerotic bone. The temporal evolution of Modic changes is uncertain, but the time span is years. Subchondral bone marrow signal changes associated with pain can be observed in different specific infectious, degenerative and immunological diseases such as osseous infections, osteoarthritis, ankylosing spondylitis and spondylarthritis. In the vertebrae, Modic changes are seen in relation to vertebral fractures, spondylodiscitis, disc herniation, severe disc degeneration, injections with chymopapain, and acute Schmorl’s impressions. The aim of this paper is to propose two possible pathogenetic mechanisms causing Modic changes. These are: A mechanical cause: Degeneration of the disc causes loss of soft nuclear material, reduced disc height and hydrostatic pressure, which increases the shear forces on the endplates and micro fractures may occur. The observed Modic changes could represent oedema secondary to the fracture and subsequent inflammation, or a result of an inflammatory process from a toxic stimulus from the nucleus pulposus that seeps through the fractures. A bacterial cause: Following a tear in the outer fibres of the annulus e.g. disc herniation, new capilarisation and inflammation develop around the extruded nuclear material. Through this tissue it is possible for anaerobic bacteria to enter the anaerobic disc and in this environment cause a slowly developing low virulent infection. The Modic changes could be the visible signs of the inflammation and oedema surrounding this infection, because the anaerobic bacteria cannot thrive in the highly aerobic environment of the Modic changes type 1. Perspectives: One or both of the described mechanisms can – if proven – be of significant importance for this specific subgroup of patients with low back pain. Hence, it would be possible to give a more precise and relevant diagnosis to 20-50% of patients with low back pain and enable in the development of efficient treatments which might be antibiotics, special rehabilitation programmes, rest, stabilizing exercise, or surgical fixation, depending on the underlying cause for the Modic changes.
