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Neurology India, Vol. 59, No. 3, May-June, 2011, pp. 331-332 Editorial Diffusion-weighted imaging signal hyperintensity in subacute combined degeneration of the spinal cord Basant K Puri Department of Imaging, Hammersmith Hospital and Imperial College, London, United Kingdom Correspondence Address: Basant K Puri Department of Imaging, Hammersmith Hospital, Du Cane Road, London W12 0HS, England United Kingdom basant.puri@imperial.ac.uk Date of Submission: 26-May-2011 Code Number: ni11104 PMID: 21743157 DOI: 10.4103/0028-3886.82708 Vitamin B 12 deficiency may lead to demyelination in the cerebrum or spinal cord, with the latter resulting in subacute combined degeneration, which reflects demyelination of the peripheral nerves, posterior columns, and lateral corticospinal tracts. [1] The term subacute combined degeneration of the spinal cord was introduced in 1900: "By combined degeneration of the spinal cord is meant an affection in which tracts of different function are concomitantly affected. It is, therefore, obvious that under such a title might legitimately be included a variety of different affections, each of which is characterised by the concomitant implication of tracts of different function. ...We…must trust to the 'Subacute' as being sufficient to exclude most other forms of combined degenerations of the spinal cord …" [2] Vitamin B 12 deficiency is also associated with pernicious anaemia; in 1926, Milnot and Murphy showed that this could be controlled by eating liver, while in 1948 red cobalt-containing crystals of this vitamin were obtained almost simultaneously by two pharmaceutical companies from liver extracts. [3] Intramuscular injection of this vitamin, for example in the form of the naturally occurring hydroxocobalamin (which contains a hydroxyl ion attached to cobalt) or the synthetic form cyanocobalamin (in which the cyanide ion CN - is attached to cobalt), may be sufficient to bring about remission of subacute combined degeneration; improvement may not occur for months, and up to 18 months may be required for full improvement, but if treatment is started early, before axonal loss has taken place, recovery may be complete. [1],[3] After a fortnight's treatment with vitamin B 12 , folic acid should usually be added; also, potassium levels should be checked periodically, owing to the risk of hypokalaemia developing early in the course of the vitamin B 12 treatment. [1] Given the potential treatability of subacute combined degeneration of the spinal cord, it is important to be able to diagnose this condition as soon as possible. Hence the need for a good diagnostic marker in magnetic resonance imaging (MRI) scans of the spinal cord. To this end, it is noteworthy that T2-weighted structural MRI scans of the spinal cord have been reported to show abnormally high signal intensity in the posterior columns, including in a particularly instructive case report and literature review by Srikanth and colleagues. [4],[5] Diffusion-weighted imaging (DWI), which provides qualitative and quantitative functional information concerning the microscopic diffusion of water molecules at the cellular level, has been widely used for the evaluation of a variety of brain disorders, including acute stroke, and of a number of musculoskeletal disorders, including vertebral fractures, bone marrow infection, bone marrow malignancy, primary bone and soft tissue tumours, and post-treatment follow-up. [6],[7] This issue of Neurology India includes the first report of the use of spinal cord DWI in subacute combined degeneration, in a paper entitled "Hyperintense signal on spinal cord DWI in a patient with subacute combined degeneration" by Chenglin Tian. [8] As implied by the title, this paper reports that a hyperintense signal is detected on spinal cord DWI in this disorder. Clearly, it is important that this case report be replicated in further, larger, studies before this finding can be used diagnostically. Furthermore, hyperintense signals in the posterior columns of the spinal cord in T2-weighted images have been reported as disappearing on recovery from subacute combined degeneration; [4] it would be good to know whether or not the hyperintense DWI spinal cord signal likewise returns to normal following successful treatment, so that spinal cord DWI can be used to help monitor treatment response. One hopes that it will not be too long before the answers to both of these important questions are known. References
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