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Adult Leukodystrophies: a Step- By-Step Diagnostic Approach

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This copy is for personal use only. To order printed copies, contact [email protected] 153 NEUROLOGIC/HEAD A Adult Leukodystrophies: A Step- by-Step Diagnostic Approach Lucas Lopes Resende, MD N Anderson Rodrigues Brandão de Paiva, Leukodystrophies usually affect children, but in the last several D NECK MD decades, many instances of adult leukodystrophies have been re- Fernando Kok, MD, PhD ported in the medical literature. Because the clinical manifestation Claudia da Costa Leite, MD, PhD of these diseases can be nonspecific, MRI can help with establish- Leandro Tavares Lucato, MD, PhD ing a diagnosis. A step-by-step approach to assist in the diagnosis I of adult leukodystrophies is proposed in this article. The first step MAGI Abbreviations: CADASIL = cerebral auto- is to identify symmetric white matter involvement, which is more somal dominant arteriopathy with subcortical commonly observed in these patients. The next step is to fit the infarcts and leukoencephalopathy, CTX = cere- N brotendinous xanthomatosis, FLAIR = fluid-at- symmetric white matter involvement into one of the proposed pat- G tenuated inversion recovery, X-ALD = X-linked terns. However, a patient may present with more than one pattern adrenoleukodystrophy of white matter involvement. Thus, the third step is to evaluate for RadioGraphics 2019; 39:153–168 five distinct characteristics—including enhancement, lesions with https://doi.org/10.1148/rg.2019180081 signal intensity similar to that of cerebrospinal fluid, susceptibility- Content Codes: weighted MRI signal intensity abnormalities, abnormal peaks at MR spectroscopy, and spinal cord involvement—to further narrow From the Neuroradiology Section, Instituto de Radiologia (InRad), Hospital das Clínicas, Facul- the differential diagnosis. dade de Medicina da Universidade de São Paulo © (HC-FMUSP), R. Dr. Ovídio Pires de Campos RSNA, 2019sradiographics.rsna.org 75, São Paulo, SP 05403-010, Brazil (L.L.R., C.d.C.L., L.T.L.); and Neurogenetics Unit, De- partment of Neurology, Hospital das Clínicas da Universidade de São Paulo, São Paulo, Brazil (A.R.B.d.P., F.K.). Recipient of a Certificate of Introduction Merit award for an education exhibit at the 2017 RSNA Annual Meeting. Received March 12, Leukodystrophies currently are defined as genetically determined 2018; revision requested May 8 and received July disorders that primarily affect the white matter of the central nervous 3; accepted July 23. For this journal-based SA- system, regardless of the structural white matter component, molec- CME activity, the authors C.d.C.L. and L.T.L. have provided disclosures; all other authors, the ular process, patient age group, and disease course involved. Genetic editor, and the reviewers have disclosed no rele- testing is of paramount importance (1). vant relationships. Address correspondence to L.L.R. (e-mail: [email protected]). Although these disorders primarily manifest in early infancy and childhood, they may also affect adults, who occasionally present with ©RSNA, 2019 clinical and imaging findings that are distinct from those observed in children (2,3). There is growing recognition that leukodystrophies SA-CME LEARNING OBJECTIVES may manifest initially during adulthood (4). After completing this journal-based SA-CME Adult leukodystrophies usually are progressive diseases. Patients activity, participants will be able to: may present with movement disturbance, vision problems, hearing ■ Discuss a framework that could help impairment, imbalance, memory loss, behavioral changes, and atten- radiologists and clinicians narrow the usually broad differential diagnosis for tion deficits (5–8). adult patients suspected of having leuko- Because the clinical manifestation of leukodystrophy can be non- dystrophy. specific, MRI has been used as a powerful paraclinical tool; it some- ■ Identify the imaging features of some of times can be the key to narrowing the diagnosis, even at the early the most prevalent adult leukodystrophies. stages of the disease in presymptomatic patients and carriers (5,7). ■ Describe the key image points that might Symmetric involvement in the white matter at MRI is an essential lead to a confirmed diagnosis in patients suspected of having adult leukodystrophies. finding in patients with adult leukodystrophies, because it commonly is associated with inherited disorders. However, the imaging pattern See rsna.org/learning-center-rg. of adult leukodystrophy can vary according to the disease and its time course (9,10). In addition to symmetry, many other MRI features can help in reaching a final diagnosis in patients who are presumed to have adult leukodystrophy or at least in narrowing the list of diagnoses for which to evaluate as part of the differential diagnosis. An algorithm that allows evaluation of all of these characteristics has been devel- oped to help differentiate among white matter diseases overall (11). 154 January-February 2019 radiographics.rsna.org TEACHING POINTS In addition to recognizing symmetric white matter involvement, characterizing the white mat- ■ Symmetric involvement in the white matter at MRI is an es- ter involvement pattern is necessary to continue sential finding in patients with adult leukodystrophies, be- cause it commonly is associated with inherited disorders. with the differential diagnosis. ■ T2-weighted and fluid-attenuated inversion-recovery (FLAIR) MRI are the best sequences to use to determine white matter Step 2: Look for a White Matter involvement. Involvement Pattern ■ Sometimes the same patient presents with more than one The next step in the diagnostic approach is to pattern during the time course of the disease, and a given leu- look for the pattern of white matter involvement. kodystrophy may manifest with more than one of these pat- There are six patterns of white matter involve- terns. In this situation, searching for distinctive findings (step ment with which radiologists should be aware to 3) will help to restrict the conditions to consider in the dif- ferential diagnosis and target the specific confirmatory tests. reduce the list of possible diagnoses, as shown in ■ The periventricular pattern is probably the most prevalent of Figure 2. However, sometimes the same patient all patterns, and myriad distinct diseases, including diseases presents with more than one pattern during the other than leukodystrophies, can manifest with periventricular time course of the disease, and a given leukodys- involvement. trophy may manifest with more than one of these ■ MR spectroscopy might be used as a potential noninvasive patterns. In this situation, searching for distinc- biomarker of treatment response in treatable diseases such tive findings (step 3) helps to restrict the condi- as CTX. tions to consider in the differential diagnosis and target the specific confirmatory tests. The purpose of this review is to adapt this Parieto-occipital Pattern algorithm for adult leukodystrophies and to demonstrate the imaging features of some of the X-linked Adrenoleukodystrophy.—X-linked most prevalent forms of this disease. The ap- adrenoleukodystrophy (X-ALD), one of the most proach we propose here must be used mainly as common adult leukodystrophies, is caused by a a framework. The characterization of all possible mutation in the adenosine triphosphate–binding types of leukodystrophies and eventual atypical cassette subfamily D member 1 gene (ABCD1), presentations is beyond the scope of this review. which codes for an adenosine triphosphate–bind- ing cassette transporter and is located in the per- Step 1: Identify Symmetric White oxisomal membrane. The biochemical hallmark Matter Involvement of this condition is an elevation in serum levels Symmetric white matter involvement at MRI is a of very long-chain fatty acids, which also accu- typical finding in patients with leukodystrophies. mulate in neural tissues and in the adrenal gland. Thus, recognizing this involvement is important Molecular confirmation of X-ALD is performed when leukodystrophies are suspected, although by sequencing the ABCD1 gene (10,13,14). there are exceptions to this pattern (12). T2- In adults, there are different forms of X-ALD. weighted and fluid-attenuated inversion-recovery The most common is “pure” adrenomyeloneu- (FLAIR) MRI are the best sequences to use to ropathy, which manifests with slowly progres- determine white matter involvement, as shown in sive spastic paraparesis, sensory disturbances, Figure 1, which illustrates symmetric white mat- and bladder dysfunction. These patients usu- ter involvement compared with an asymmetric ally experience spinal cord atrophy, mainly in pattern. White matter lesions appear as hyperin- its thoracic segment, but the brain shows no tensity on T2-weighted and FLAIR MR images abnormalities. The cerebral manifestation of and hypo- or isointensity on T1-weighted images. X-ALD is less frequent in adults and is char- Depending on the cause and stage of the disease, acterized by psychiatric features followed by signal intensity may vary. Familiarity with typical dementia, ataxia, seizures, and even death. In manifestations is important (13). these patients, MR images of the brain are simi- Important exceptions to this rule are geneti- lar to those observed in children with ALD, and cally defined vasculopathies, such as CADA- the spinal cord shows no abnormalities. Other SIL, in which abnormalities in signal intensity patients present with intermediate forms of the (ie, increased signal intensity on T2-weighted disease that include involvement of the spinal or FLAIR MR
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