Letters to the Editor What is the role of proton MR spectroscopy of the lumbar spine in patients with glycogen storage disease type Ib? We read with interest the article by Scherer et al in the December 2001 issue of JMRI (1). The authors report on the use of proton MR spectroscopy to evaluate the water-to-lipid ratio as a quantitative means of charac- terizing vertebral marrow in Glycogen Storage Disease (GSD) Ib patients, with and without treatment. The introduction is a well-done and comprehensive explanation of GSD type Ib and the effect of treatment on this disease. Nonetheless, the body of the article has, we believe, several weaknesses. The authors present characteristics and results of quantitative proton MR spectroscopy in the vertebral body L1 in healthy volunteers and in GSD Ib patients. They also include figures with spectra showing in- creased water signal and an almost complete loss of lipid signal in the bone marrow of the L1 vertebral body in patients with GSD Ib. These findings are well known and have been published previously in different jour- nals; for example, in an article in the August 2001 issue of AJR by the same authors (2). It is surprising, how- ever, that the authors do not correlate their findings with MR imaging findings. In the August 2001 article the authors conclude that in patients with GSD Ib, an increased myelopoetic activity of bone marrow caused by functionally impaired leukocytes can be shown by MR imaging (2). It is puzzling, to say the least, that they failed to reiterate that important point in the current article. Also surprising, is that in the first paragraph of the discussion they state that low signal intensity on T1- weighted images is not necessarily a sign of high mar- row cellularity, since osteomyelofibrosis and osteomy- elosclerosis result in low signal in the presence of low cellularity (1). The first part of this statement is quite true. On the other hand, attempting to diagnose myelo- fibrosis with only one T1-weighted sequence is quite wrong. In our review of imaging findings in patients with myelofibrosis, we stress that to diagnose myelofi- brosis, MR imaging must demonstrate a very low signal and a mainly homogeneous signal in both T1- and T2- weighted images (3). The T2-weighted sequence is very important since diminution of marrow signal intensity on T1-dependent pulse sequences is also shared by other pathologies such as tumors, osteomyelitis, and metastases of various origins. Therefore, shorter T1 is less specific for bone pathologies. Moreover, T2- weighted images are considered more specific in the case of myelofibrosis, since tumors and acute inflam- mation present longer T2, with increasing signal inten- sity, whereas fibrosis diminishes signal intensity (3). The authors conclude that in patients with GSD Ib, the proliferation of myelopoieitic cells causes a nearly complete displacement of lipid cells in the central bone marrow and that no further increase of water content can be demonstrated in GSD Ib patients undergoing treatment. As this is a conclusion, what guidelines do the authors propose for diagnosing or treating patients with GSD Ib? It seems that publishing this article after, rather than concurrently with, the August article could be mislead- ing, as in that paper they suggested MR imaging as a tool for monitoring treatment in patients with GSD Ib. Ali Guermazi, MD, Bachir Taouli, MD, Lynne S. Steinbach, MD, Harry K. Genant, MD. Department of Radiology, University of California, San Francisco Correspondence: Ali Guermazi Department of Radiology University of California, San Francisco 350 Parnassus Ave, Suite 150 San Francisco, CA 94117 Tel: (415) 476-4524 Fax: (415) 502-2486 E-mail: ali.guermazi@oarg.ucsf.edu REFERENCES 1. Scherer A, Wittsack HJ, Engelbrecht V, Schwarz S, May P, Poll LW, Koch JA, Wendel U, Modder U. Proton MR spectroscopy of the lum- bar spine in patients with glycogen storage disease type Ib. J Magn Reson Imaging 2001;14:757-762. 2. Scherer A, Engelbrecht V, Neises G, May P, Balsam A, Spiekerkotter U, Wendel U, Modder U. MR imaging of bone marrow in glycogen storage disease type IB in children and young adults. AJR Am J Roentgenol. 2001;177:421-425. 3. Guermazi A, de Kerviler E, Cazals-Hatem D, Zagdanski AM, Frija J. Imaging findings in patients with myelofibrosis. Eur Radiol 1999;9: 1366-1375. DOI 10.1002/jmri.10160 Published online in Wiley InterScience (www.interscience.wiley.com). Reply: Guermazi et al. make reference to results from two articles of our research group (1,2) which are seemingly contradictory for them. The articles deal with the eval- uation of bone marrow in glycogen storage disease type Ib (GSD Ib). In our first article we reported on marked bone mar- row signal changes in T1 and T2 as well as short tau JOURNAL OF MAGNETIC RESONANCE IMAGING 16:330 –331 (2002) © 2002 Wiley-Liss, Inc. 330