Acute reversible toxic leukoencephalopathy - A different entity

S Srinivasan, SZ Ali 
 Department of Diagnostic Radiology, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore 768228, Singapore

Correspondence Address:
S Srinivasan
Department of Diagnostic Radiology, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore 768228
Singapore

Full Text

Sir,

We read with great interest the report of a case of leukoencephalopathy induced by chemotherapeutic agents. [1] It should be noted that such leukoencephalopathies are different from reversible posterior leukoencephalopathy syndrome (RPLS), which is otherwise known as posterior reversible encephalopathy syndrome (PRES). RPLS classically occurs in conditions associated with sudden elevation of blood pressure, and magnetic resonance (MR) imaging usually shows vasogenic edema in the parieto-occipital white matter. [2] Typical RPLS does not show restricted diffusion on diffusion-weighted MR (DW-MR) imaging sequence. [2] The white matter changes associated with chemotherapeutic agents are not confined to parieto-occipital region and, hence, the condition is classified under acute reversible toxic leukoencephalopathy [3],[4] which is a different entity. Previously, they were mistakenly called as atypical forms of PRES or RPLS. [5]

Because of increasing use of chemotherapeutic agents such as 5-fluorouracil (5-FU), such leukoencephalopathies are being increasingly reported recently [3],[4] and are not so rare as stated by the authors. One reason could be the lack of search of recent radiological literature by the authors.

Diffusion restriction in the white matter is not due to vasogenic edema (as mentioned by the authors). In simple vasogenic edema, there would be unrestricted movement of the hydrogen molecules (also known as protons) and, hence, would not cause restriction of diffusion in DW-MR imaging. In toxic leukoencephalopathy, the etiology of restricted diffusion is presumed to be intramyelinic edema, endothelial damage, and cytotoxicity or direct demyelination. [3]

Another teaching point which we would like to emphasize is that the restricted diffusion disappears after stopping the chemotherapeutic agent, as noted by Sivasubramanian et al. [3] and Mckinney et al. , [4] although authors have acknowledged that they could not repeat the MR imaging due to patient's refusal.

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