(Stroke. 1996;27:1420-1423.)
© 1996 American Heart Association, Inc.
Articles |
Adult-Onset MELAS
Evidence for Involvement of Neurons as Well as Cerebral Vasculature in Strokelike Episodes
the Departments of Neurology (J.M.G.) and Pathology (M.S., E.S.), Rhode Island Hospital, Brown University School of Medicine, Providence, RI; and the H. Houston Merritt Clinical Research Center for Muscular Dystrophy and Related Diseases, Columbia-Presbyterian Medical Center, New York, NY (S.S.).
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Abstract |
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 Top Abstract IntroductionCase ReportDiscussionReferences |
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Background We report a 46-year-old woman with implications regarding pathogenesis of strokelike episodes in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes). She had a 10-month history of episodic seizures, strokes, cognitive decline, vomiting, and ileus. She also had sensorineural hearing loss, insulin-dependent diabetes mellitus of several years' duration, and persistent lactic acidosis. Family history was pertinent for a similar syndrome in her deceased mother (onset in her sixties), for hearing loss and diabetes mellitus in two brothers, and for hearing loss in her only child, a son.
Case Description Serial MRIs of the brain revealed severe but evanescent cerebral cortical abnormalities. A left temporal brain biopsy was performed to exclude encephalitis. Light microscopy revealed a diffuse fibrillary gliosis with abundant reactive gemistocytes, focal evidence of ischemic neuronal injury, and edema. Electron microscopy revealed bizarre enlarged mitochondria and changes consistent with cellular edema. Succinate dehydrogenase staining was strongly reactive within cerebral blood vessels and within neurons. A point mutation was subsequently found at nt 3243 of the mitochondrial tRNALeu(UUR) gene in peripheral leukocytes and in brain, confirming the clinical diagnosis of MELAS. Quantitation revealed that 82% of brain mitochondria carried the disease mutation, indicating that most, if not all, tissues were affected.
Conclusions Our findings suggest that strokelike episodes in MELAS result from defects in neuronal metabolism, as well as in cerebral vasculature.
Key Words: mitochondrial encephalomyopathies • neuronal damage • pathology • stroke, acute
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Introduction |
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In 1984, Pavlakis et al1 reported two cases and collected nine more from the literature that had in common several characteristics: mitochondrial encephalomyopathy, lactic acidosis, and recurrent strokelike episodes (MELAS). Several series of cases have been reported since with clarification of the clinical characteristics, biochemistry, and genetics.2 3 4 5 6 7 8 In 1990, Goto et al9 reported a mutation in mitochondrial DNA in most but not all MELAS patients. This was a point mutation affecting the transfer RNA for leucine (nucleotide 3243 of mitochondrial tRNALeu(UUR). This mutation has been confirmed in other MELAS patients in 60% to 90% of cases.2 5 7 A separate point mutation at another locus of the same gene has been discovered in a small number of MELAS patients.10 Mitochondrial genes code for approximately 15% of the electron transport chain, but no specific enzyme defect in that chain has been found for MELAS; rather, a variety of defects has been seen.5 This pattern is true for other mitochondrial defect syndromes, none of which has a specific biochemical abnormality. The muscle pathology is well defined, but that of brain is not; all of the prior reports relate to postmortem tissue11 12 13 14 15 16 and precede the ability to genetically confirm the diagnosis. Pathogenesis of the strokelike episodes is controversial.14 15 16 17 We wish to report a case of adult-onset MELAS (itself uncommon) and give a detailed report of the antemortem brain, with implications for theories of pathogenesis.
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Case Report |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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The patient was a 46-year-old woman who was transferred to Rhode Island Hospital on February 25, 1994, from another hospital where she had been admitted with acute mental status changes. One week before admission she had a significant change in cognition, and on February 21 she was seen in the emergency department at the other hospital, where she was found to be hallucinating and to have incoherent speech. A CT of the head at that time showed mild cortical atrophy, and an electroencephalogram revealed generalized slow wave activity.
Her past medical history was remarkable for insulin-dependent diabetes mellitus and sensorineural hearing loss since her early thirties. She had a similar episode with significant mental status changes and apparent partial complex seizures with secondary generalization in May 1993. CT of the head then showed a right temporal lesion, which was felt to be either infarction or tumor. She improved and had no further seizures while being treated with phenytoin. As an outpatient, she was referred to a neurosurgeon who obtained an MRI of the head, which was interpreted as either right temporal infarction or glioma (Fig 1
, left). Repeated MRI in July 1993 showed resolution of the abnormality, with only a few punctate areas of signal abnormality in the right corona radiata. Another MRI in October 1993 was normal. Her diagnosis was retrospectively changed to encephalitis. She had no prior history of psychological or neurological illness.
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Her family history was also remarkable: her mother had a similar syndrome in her early sixties that led to her death at age 62. The patient's mother and two of her three brothers had hearing loss beginning in the second and third decades, as well as insulin-dependent diabetes mellitus. Her only child, a son, had hearing loss since age 12 years (Fig 2).
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After admission to Rhode Island Hospital, the patient continued to be incoherent, agitated, and unresponsive to any attempts to communicate. She remained alert but was unable to feed herself or take care of her activities of daily living. Her neurological examination was nonfocal, with no limb weakness or gross visual field defects, and she had intact and symmetrical deep tendon reflexes and bilateral negative Babinski reflexes. She could walk with no assistance. She had a transient episode of vomiting lasting 2 days early in her course but recovered spontaneously. By day 11 of hospitalization she began to show cognitive improvement, and over the next 2 weeks she became more coherent. Her language function evolved into a fluent aphasia with frequent spoken and written paraphasias and reading and verbal comprehension defects. She was able to feed herself and participate in her daily care. However, recurrent episodic vomiting and ileus hampered her nutritional status, and a perendoscopic gastrostomy was performed for feeding-tube placement. She was given riboflavin and nicotinamide via gastrostomy without obvious clinical benefit.6
Laboratory examination was extensive. Complete blood count, electrolyte levels, liver function tests, blood urea nitrogen, and creatinine levels were all normal. Serum glucose was elevated. Serum lactate was abnormal on numerous occasions, varying from 3.5 to 4.8 mEq/L (normal is <1.3). Cerebrospinal fluid examination shortly after admission was normal, with no white blood cells and a normal protein of 50 mg/dL. Herpes simplex titers in the cerebrospinal fluid were normal. Electroencephalography showed slow waves, greater over the left hemisphere, but no periodic waves or spike discharges. MRI of the brain revealed cortical signal abnormality involving the left temporal, parietal, insular, and occipital lobes, with gyral swelling but no mass effect (Fig 1
, middle). Gadolinium infusion showed patchy, punctate enhancement (Fig 1, right). To exclude encephalitis,18 a left temporal brain biopsy was performed. Brain and peripheral blood leukocyte samples were analyzed for the presence of mitochondrial mutations; both revealed a mutation at nt 3243 of the mitochondrial tRNALeu(UUR) gene, more prevalent in the brain (82%) than blood (23%) (Table). Two of the patient's brothers (one asymptomatic) and her son also had mutation analysis performed on peripheral leukocytes (Table).
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Methods
To detect the point mutation in the tRNALeu(UUR) gene of mtDNA (an A
G transition at nt 3243), we used oligonucleotide primers corresponding to positions nt 3116-3134 (forward) and nt 3353-3333 (backward) to amplify by PCR a DNA fragment spanning the putative mutation. One microliter of [
-32P]dATP (3000 Ci/mmol) was added before the last cycle to the PCR mixture to label the PCR product. This 238-bp fragment was digested with the restriction enzyme Hae III. The point mutation creates an additional Hae III site, thus providing a simple molecular test for this genetic defect. The digested DNA was electrophoresed through a 12% nondenaturing polyacrylamide gel, dried, and autoradiographed at room temperature for 1 hour using Kodak XAR5 film without intensifying screen. To quantify the relative amount of normal and mutant DNA, the gels were scanned for 1 hour in a Betascope 603 blot analyzer (Betagen). The amount of mutant DNA was expressed as the percentage of total Hae III–cleaved material [(label of 97-bp+72-bp fragments)/(label of 169-bp+97-bp+72-bp fragments)x100].
Brain Pathology
Hematoxylin and eosin–stained sections of the biopsy revealed diffuse fibrillary gliosis with abundant reactive gemistocytes. The changes were evident in both cortex and white matter and were associated with diffuse edema. Many degenerative pyknotic-appearing neurons were seen in the cerebral cortex. Two small vessels displayed perivascular cuffing with chronic inflammatory cells. On Luxol fast blue stain there was no evidence of demyelination. No intranuclear or intracytoplasmic inclusions were seen. Immunohistological stains for toxoplasmosis, herpes virus, and cytomegalovirus were negative.
SDH stains were strongly positive within the smooth muscle cells of small arterioles (Fig 3, top). A punctate pattern of SDH staining was also seen within the surrounding neurons, suggestive of collections of abnormal mitochondria (Fig 3, bottom). SDH brain tissue controls did not show a significant increase in staining (not shown). Electron microscopy was performed, and numerous small intracellular vacuoles filled with fine granular debris were seen. A number of bizarre-appearing mitochondria were identified within neurons, with irregular and sometimes concentric cristae but without paracrystalline inclusions (Fig 4). Similarly abnormal mitochondria were also identified within smooth muscle and endothelial cells of small arterioles (not shown).
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Discussion |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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Brain pathology has been poorly characterized in MELAS primarily because all of the previously reported cases were postmortem, with end-stage ischemic changes as the dominant feature.11 12 13 14 15 16 Also, all but one of the prior reports predated the ability to confirm the diagnosis of MELAS with mitochondrial mutation testing. Several of these cases had features suggesting more than one of the mitochondrial syndromes, and it is possible that the patients in question actually had MERRF19 20 or Kearns-Sayre syndrome21 rather than MELAS. Only a single prior report details the ultrastructural examination of the brain in MELAS,14 and it is also the only report of involvement of cerebral blood vessels.14 Abnormalities were restricted to pial arterioles (up to 50 µm in diameter) and small arteries (up to 250 µm). Intracerebral arterioles and small arteries were not affected, and large arteries were normal. The light and electron microscopic findings were found primarily in smooth muscle cells and only infrequently in endothelial cells; these findings included microvacuolization, fiber size variation, pyknosis, increased number of mitochondria, and structural abnormalities of mitochondria, although paracrystalline inclusions were not found.
Various theories exist about the etiology of the strokelike episodes in MELAS. One of the two most frequently invoked is that the cells themselves become metabolically deranged and cannot function, with subsequent failure of energy production. This has been supported by 31P nuclear MR spectroscopy of muscle6 and by cerebral blood flow studies.17 The other theory is that blood vessels are involved, with resultant malfunction and downstream ischemia.14 15 16 23 Evidence for this includes strongly positive SDH staining of intramuscular arterioles, which correlates with the presence of abnormal mitochondria in the vessel walls23 24 25 26 and abnormalities of cerebral pial arterioles and small arteries.14 Smooth muscle cells in the vessel wall are most often involved, with endothelial cells either not involved or to a much lesser degree. The lack of neuronal or glial mitochondrial abnormalities14 19 has been used as support of the mitochondrial vasculopathic-induced ischemia theory. However, this theory fails to explain widespread cortical involvement on the basis of small-vessel disease.
We were able to establish the presence of MELAS in an antemortem brain biopsy from this patient using PCR and the techniques of modern molecular biology, as well as supportive evidence from light and electron microscopy. The location of the abnormal mitochondria was within the smooth muscle of cerebral blood vessel walls and within cells of the central nervous system. Evidence for this observation comes from the SDH staining, and the electron microscopic images of abnormal mitochondria within neuronal, smooth muscle, and endothelial cells. Another piece of evidence supporting this contention is that 82% of brain mitochondrial DNA carried the point mutation at nt 3243. Such a high percentage of mutated DNA most likely suggests that the mutations are carried within a large proportion of the total mitochondrial complement of the affected brain tissue. It is unlikely that such a high percentage of mutated DNA could reside solely within blood vessels, which provide only a small percentage of the total mitochondria of brain. The mutations must also reside in more numerous cells such as neuroglia and neurons. MELAS may involve the brain more completely than by a simple effect on vascular performance and integrity alone.
We conclude that MELAS represents widespread cellular dysfunction, not restricted to either neuronal or vascular derangement.
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Selected Abbreviations and Acronyms |
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Footnotes |
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Reprint requests to Dr Gilchrist, 593 Eddy St, APC 689, Providence, RI 02903.
Received March 18, 1996; revision received April 29, 1996; accepted April 29, 1996.
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References |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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