Mitochondrial Strokes: Diagnostic Challenges and Chameleons

Mitochondrial stroke-like episodes (SLEs) are a hallmark of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). They should be suspected in anyone with an acute/subacute onset of focal neurological symptoms at any age and are usually driven by seizures. Suggestive features of an underlying mitochondrial pathology include evolving MRI lesions, often originating within the posterior brain regions, the presence of multisystemic involvement, including diabetes, deafness, or cardiomyopathy, and a positive family history. The diagnosis of MELAS has important implications for those affected and their relatives, given it enables early initiation of appropriate treatment and genetic counselling. However, the diagnosis is frequently challenging, particularly during the acute phase of an event. We describe four cases of mitochondrial strokes to highlight the considerable overlap that exists with other neurological disorders, including viral and autoimmune encephalitis, ischemic stroke, and central nervous system (CNS) vasculitis, and discuss the clinical, laboratory, and imaging features that can help distinguish MELAS from these differential diagnoses.

Progressive External Ophthalmoplegia in Polish Patients-From Clinical Evaluation to Genetic Confirmation

Mitochondrial encephalomyopathies comprise a group of heterogeneous disorders resulting from impaired oxidative phosphorylation (OxPhos). Among a variety of symptoms progressive external ophthalmoplegia (PEO) seems to be the most common. The aim of this study is to present clinical and genetic characteristics of Polish patients with PEO. Clinical, electrophysiological, neuroradiological, and morphological data of 84 patients were analyzed. Genetic studies of mitochondrial DNA (mtDNA) were performed in all patients. Among nuclear DNA (nDNA) genes POLG was sequenced in 41 patients, TWNK (C10orf2) in 13 patients, and RNASEH1 in 2 patients. Total of 27 patients were included in the chronic progressive external ophthalmoplegia (CPEO) group, 24 in the CPEO+ group. Twenty-six patients had mitochondrial encephalomyopathy (ME), six patients Kearns-Sayre syndrome (KSS), and one patient sensory ataxic neuropathy, dysarthria, ophthalmoparesis (SANDO) syndrome. Genetic analysis of nDNA genes revealed the presence of pathogenic or possibly pathogenic variants in the POLG gene in nine patients, the TWNK gene in five patients and the RNASEH1 gene in two patients. Detailed patients' history and careful assessment of family history are essential in the diagnostic work-up. Genetic studies of both mtDNA and nDNA are necessary for the final diagnosis of progressive external ophthalmoplegia and for genetic counseling.

Successful liver transplantation in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal disorder characterized by progressive gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, skeletal myopathy, ophthalmoparesis, and ptosis. MNGIE stems from deficient thymidine phosphorylase activity (TP) leading to toxic elevations of plasma thymidine. Hematopoietic stem cell transplant (HSCT) restores TP activity and halts disease progression but has high transplant-related morbidity and mortality. Liver transplant (LT) was reported to restore TP activity in two adult MNGIE patients. We report successful LT in four additional MNGIE patients, including a pediatric patient. Our patients were diagnosed between ages 14 months and 36 years with elevated thymidine levels and biallelic pathogenic variants in TYMP. Two patients presented with progressive gastrointestinal dysmotility, and three demonstrated progressive peripheral neuropathy with two suffering limitations in ambulation. Two patients, including the child, had liver dysfunction and cirrhosis. Following LT, thymidine levels nearly normalized in all four patients and remained low for the duration of follow-up. Disease symptoms stabilized in all patients, with some manifesting improvements, including intestinal function. No patient died, and LT appeared to have a more favorable safety profile than HSCT, especially when liver disease is present. Follow-up studies will need to document the long-term impact of this new approach on disease outcome. Take Home Message: Liver transplantation is effective in stabilizing symptoms and nearly normalizing thymidine levels in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and may have an improved safety profile over hematopoietic stem cell transplant.

Mitochondrial A3243G mutation causes mitochondrial encephalomyopathy in a Chinese patient: Case report

RATIONALE

Mitochondrial mutations are associated with a wide spectrum of clinical abnormalities. More than half of these mutations are distributed in the 22 mitochondrial tRNA genes, including tRNA. In particular, the A3243G mutation in the tRNA gene causes mitochondrial encephalomyopathy.

PATIENT CONCERNS

A 12-year-old boy was admitted to Shaoxing People's Hospital because there is a reduction in the volume of speech, dysphonia, unable to write, recognize words, and unable to wear clothes, accompanied by unstable walking after treatment of unexplained fever and somnolence.

DIAGNOSES

The proband underwent a thorough examination in our hospital and was diagnosed as mitochondrial encephalomyopathy. The proband carried the pathogenic heteroplasmic mutation A3243G mutation in mitochondrial 12S rRNA gene. Although his parents did not carry the mutation.

INTERVENTIONS

Intravenous acyclovir, ceftriaxone, and dexamethasone were used for the patient's antiviral, antimicrobial, and anti-inflammatory therapy, respectively. Intravenous mannitol was gradually tapered for reducing intracranial pressure with furosemide for inducing diuresis. Intravenous arginine could help to treat alkalosis and supple some essential amino acids. Oral oxiracetam capsules, vitamin B1, and coenzyme Q10 were used for providing nutrition and improving energy. His medications were 30 mg vitamin B1, 0.1 g vitamin C, and mecobalamin 750 μg daily after discharge from our hospital.

OUTCOMES

The patient was able to walk and talk slowly with improved writing skills and no stroke-like episodes. The neurological examination was negative and muscle tension was identified as grade V.

LESSONS

Mitochondrial encephalomyopathy has different phenotypes, in addition to traditional examinations, it is important for clinicians to be familiar with genetic testing methodology as well as applications of these tests in clinic to get an accurate diagnosis.

Mitochondrial Cardiomyopathy with a Unique 99mTc-MIBI/123I-BMIPP Mismatch Pattern

A 42-year-old man was referred to our hospital due to chest pain, diabetes mellitus, and sensorineural hearing loss. Transthoracic echocardiography revealed diffuse left ventricular hypokinesis. He was diagnosed with mitochondrial disease and a c.A3243G mutation was identified in his mitochondrial DNA. This case of mitochondrial cardiomyopathy demonstrated a low uptake of ¹²³I-BMIPP, while the uptake of ^99mTc-MIBI was preserved. In contrast, previous reports have noted the increased uptake of¹²³I-BMIPP and the decreased uptake of ^99mTc-MIBI. This is the first study to show this unique ^99mTc-MIBI/¹²³I-BMIPP mismatch pattern. We also discuss the relationships among the cardiac scintigraphy, cardiac magnetic resonance imaging, and histopathology findings.

99-mTc-HMPAO single photon emission computed tomography examinations in genetically determined neurometabolic disorders

The aim of our study was to determine regional cerebral blood flow (rCBF) abnormalities in different types of enzymopathies.

PATIENTS AND METHODS

Among the patients with genetically determined enzymopathies 3 patients had aminoacidopathies, and 11 had different types of encephalopathies, from which 10 had mitochondrial encephalomyopathy (MEMP), and 1 patient had hyperuricaemic encephalopathy. Besides the mentioned 14 patients, 1 had ceroid lipofuscinosis and another patient had tuberous sclerosis. The further distribution of the MEMP patients' group was the following--5 patients had MEMP with lactic acidosis, 5 had Leigh's disease (subacute necrotizing encephalopathy), from which 1 had cytochrome-c-oxidase deficiency (COX). Additionally in all patients were performed cerebral MRI and SPECT examination 10 min. after intravenous administration of 20 Mbq/kg 99 mTc-HMPAO.

RESULTS

Fourteen out of 16 SPECT findings were pathologic, showing decreased focal frontal/temporal/temporoparietal cerebral blood perfusion. Aminoacidopathic group--all the 3 patients revealed pathologic signs from the aminoacidopathic patients' group. Among them the ornithine transcarbamylase (OTC) heterozygous female patient with left-sided hemiparesis caused by hyperammonemic stroke at 10 month-age, showed right sided temporoparietal, occipital and left frontal hypoperfusion, nearly 6 years after the cerebral vascular attack. This finding might be resulted because of diaschisis. Mitochondrial encephalo-myopathic (MEMP) group--all the four patients with MEMP and lactic acidosis showed focal hypoperfusion in the temporal region, while the perfusion was normal in the COX deficient patient and in 2 Leigh's disease (subacute necrotizing encephalopathy) patients. In the remaining 1 Leigh's patient frontotemporal hypoperfusion was found. In all patients there were non specific structural abnormalities detected by MRI: cortical and subcortical atrophy, and scattered demyelination foci. In the case of ceroid lipofuscinosis the MRI showed cerebral atrophy and cerebellar hypoplasia, and the SPECT showed right frontal and occipital hypoperfusion, bilateral parietal physiological riping process. The patient with tuberous sclerosis showed bilateral temporo-occipital hypoperfusion.

CONCLUSION

(1) SPECT images demonstrated hypoperfusion rCBF changes in 14 out of all 16 patients. (2) Regional cerebral/cerebellar hypoperfusion was detected by SPECT in mitochondrial encephalomyopathies, with lactate acidosis and aminoacidopathies giving high informative value about the cerebral perfusion.

Mitochondrial neurogastrointestinal encephalomyopathy in three siblings

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disorder in which a nuclear mutation of the thymidine phosphorylase (TP) gene causes mitochondrial genomic dysfunction. Patients suffer from gastrointestinal dysmotility, cachexia, ptosis, external ophthalmoparesis, myopathy and polyneuropathy. Magnetic resonance imaging (MRI) shows leukoencephalopathy. We describe clinical, genetic and neuroradiological features of three brothers affected with MNGIE. Clinical examination, laboratory analyses, MRI and magnetic resonance spectroscopy (MRS) of the brain, and genetic analysis have been performed in all six members of the family with the three patients with MNGIE. Two of them are monozygous twins. They all suffered from gastrointestinal dysmotility, cachexia, ophthalmoplegia, muscular atrophies, and polyneuropathy. Urinary thymidine was elevated in the patients related to the severity of clinical disease, and urinary thymidine (normally not detectable) was also found in a heterozygous carrier. Brain MRI showed leukoencephalopathy in all patients; however, their cognitive functioning was normal. Brain MRS demonstrated reduced N-acetylaspartate and choline in severely affected areas. MRI of heterozygous carriers was normal. A new mutation (T92N) in the TP gene was identified. Urinary thymidine is for the first time reported to be detectable in a heterozygous carrier. MRS findings indicate loss of neurons, axons, and glial cells in patients with MNGIE, but not in heterozygous carriers.

Evaluation of respiratory chain failure in mitochondrial cardiomyopathy by assessments of 99mTc-MIBI washout and 123I-BMIPP/99mTc-MIBI mismatch

Cardiomyopathy is one of the main features that determines prognosis in patients with mitochondrial encephalomyopathy. We investigated respiratory chain failure using 99mTc-MIBI- and 123I-BMIPP-SPECT in vivo in five patients with mitochondrial cardiomyopathty. With the lowering of cardiac function, the 99mTc-MIBI-washout rate (WOR) increased, and the 99mTc-MIBI-uptake decreased, conversely. In patients who showed severe cardiac involvement, 99mTc-MIBI-uptake was markedly reduced, and by contrast, 123I-BMIPP-uptake increased (123I-BMIPP/99mTc-MIBI mismatch). There were significant correlations between the WOR on 99mTc-MIBI-SPECT and interventricular septal thickness (IVST) on echocardiography and between WOR and left ventricular ejection fraction (LVEF) on 99mTc-MIBI-SPECT. The increased WOR and decreased uptake of 99mTc-MIBI were reflected by the lowered mitochondrial membrane potential created by mitochondrial respiratory chain whereas 123I-BMIPP/99mTc-MIBI mismatch may be created by the enhanced triglyceride-pool. These nuclear medicine techniques are the potential tools to evaluate the energy state in mitochondrial cardiomyopathy.

[The deaf child: anatomy, etiologies and management]

Temporal bone imaging in children shows radioanatomical aspects and diseases distinct from the imaging and pathology results found in adults. Imaging modalities such as CT and MR bring out these differences. The aim of this study is to present the CT and MR particularities of the temporal bone during postnatal growth. The mastoid air cells form mostly in the postnatal period and the course of pneumatization is directly correlated with middle ear successive inflammatory episodes. The most frequent etiologies of hearing loss in children are reviewed, emphasizing their specificities in clinical presentation, radiological aspects, and treatment. In children, conductive hearing loss with normal tympanic membrane is mostly caused by minor aplasia rather than otosclerosis. Sensorineural hearing loss, even when unilateral, is predominantly due to malformation or infection and in rare cases to posterior fossa tumor.

Abdominal pain related to mitochondrial neurogastrointestinal encephalomyopathy syndrome may benefit from splanchnic nerve blockade

Patients diagnosed with abdominal pain related to mitochondrial neurogastrointestinal encephalopathy (MNGIE) may benefit from splanchnic nerve blockade. MNGIE, varying in age of onset and rate of progression, is caused by loss of function mutation in thymidine phosphorylase gene. Gastrointestinal dysmotility, pseudo-obstruction and demyelinating sensorimotor peripheral neuropathy (stocking-glove sensory loss, absent tendon reflexes, distal limb weakness, and wasting) are the most prominent manifestations. Patients usually die in early adulthood (mean 37.6 years; range 26-58 years). We report a case of an 18-year-old patient with MNGIE. Our patient's abdominal pain was relieved after splanchnic nerve blockade.

Quantitative assessment of the total myocardial uptake ratio of 123I-BMIPP by using the Ishii-MacIntyre method is useful for predicting cardiac complications in patients with mitochondrial encephalomyopathy or myotonic dystrophy

We evaluated the usefulness of the total myocardial uptake ratio (TMUR) of 15-(p-[123I]iodophenyl)-3(R,S)-methyl-pentadecanoic acid (123I-BMIPP) for predicting cardiac complications in patients with mitochondrial encephalomyopathy or myotonic dystrophy. Six patients with mitochondrial encephalomyopathy, four with myotonic dystrophy, and 10 control subjects were studied. Quantitative assessment of 123I-BMIPP dynamic myocardial imaging was performed, and the TMUR of 123I-BMIPP was calculated according to the Ishii-MacIntyre method. Then, the TMUR was compared in the 10 patients and 10 healthy controls, and all patients were followed for 56.1+/-22.1 months to evaluate cardiac complications. TMUR in patients (2.69+/-0.64) was significantly (P =0.01) lower than that in controls (3.28+/-0.25). Three patients in whom the TMUR value was above 3.00 had no cardiac complications. On the other hand, all patients in whom TMUR was below 3.00 had some kind of cardiac complication during the follow-up period. Two patients showed progressive conduction abnormality and underwent pacemaker implantation, one patient had sick sinus syndrome and underwent pacemaker implantation, another patient showed non-sustained ventricular tachycardia and paroxysmal atrial fibrillation, and four of seven patients, including one with a pacemaker, showed an increased cardiothoracic ratio value over 50%. In conclusion, measurement of the TMUR by the Ishii-MacIntyre method is useful for evaluating the development of cardiac complications in patients with mitochondrial encephalomyopathy or myotonic dystrophy.

Diagnosis and management of MNGIE syndrome in children: case report and review of the literature

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome is a rare disorder that presents in childhood; however, marked delay in diagnosis is common. We report a case and review the literature describing the typical features that should alert pediatricians to the diagnosis. We also describe a novel management strategy for providing symptomatic relief.

[Cerebral SPECT in mitochondrial encephalomyopathy. A case report and a review of the literature]

INTRODUCTION

We report a case of mitochondrial encephalomyopathy with a complex clinical picture followed-up in the Neurology Department, and fully investigated using different techniques, in whom the definite diagnosis was essentially based on finding ragged red fibres on muscle biopsy.

CLINICAL CASE

The patient was 60 years old when the definite diagnosis was made. The illness had started in his youth and affected different systems and parts of the body. On laboratory investigation the serum lactic acid and lactic acid curve were normal, as were those of the cerebrospinal fluid. Further complementary tests were done, including imaging techniques (cerebral CAT, MR and SPECT). SPECT was done using 99Tc-HMPAO. Since it was a single case, we can affirm that the diagnosis of mitochondrial encephalomyopathy was made on muscle biopsy, supported by other complementary investigations, but without being able to classify the case among the various mitochondrial encephalopathies since the clinical features were common to several of them.

CONCLUSION

More sequential studies are needed with different imaging techniques, in the same patient, carefully taking into account any slight modification in his clinical state, during the time elapsed between two consecutive serial follow-up studies.

Impaired activation of oxygen consumption and blood flow in visual cortex of patients with mitochondrial encephalomyopathy

A current hypothesis claims that an increase of blood flow is required for oxygen consumption to rise during neuronal excitation (activation). Chronic progressive external ophthalmoplegia is a mitochondrial disease associated with deletions of mtDNA or by point mutation of tRNA genes. We tested the hypothesis that the cerebral metabolic rate of oxygen (CMRO2) may not rise in this disorder if the accompanying cerebral blood flow increase is insufficient. Two patients with progressive external ophthalmoplegia were visually stimulated with a colored checkerboard pattern reversing as different frequencies. When stimulated, Patient 1 had a small increase of cerebral blood flow, while Patient 2 had no cerebral blood flow increase. In the visually active state, the patients had no significant change of CMRO2, while healthy subjects had a pronounced increase of CMRO2 in the pericalcarine visual cortex at 4 Hz and a further slight increase at 8 Hz during activation.

Cerebral blood flow and glucose metabolism in mitochondrial disorders

OBJECTIVE

To investigate cerebral metabolism by 2-[18F]fluorodeoxy-d-glucose (FDG) uptake using PET and cerebrovascular reverse capacity by transcranial Doppler sonography (TCD) in different mitochondrial diseases (mitochondrial myopathy; mitochondrial encephalopathy, lactacidosis, and stroke-like episodes [MELAS]; and chronic external ophthalmoplegia).

BACKGROUND

Previous studies on individual patients with mitochondriopathies revealed abnormal accumulations of mitochondria in endothelium, smooth muscle cells, and pericytes of blood vessels in different parts of the nervous system (cerebrum, cerebellum, sural nerve) and skeletal muscle. On this basis, some investigators suggested a pathogenic role of vascular involvement in the MELAS syndrome and other encephalopathies. smhd1

DESIGN/METHODS

The authors investigated neuronal metabolism and cerebrovascular involvement with PET in 5 cases and with TCD with acetazolamide stimulation in 15 cases. The patients were divided into three groups: 1) interictal MELAS (n = 4); 2) progressive external ophthalmoplegia (n = 6); and 3) pure mitochondrial myopathy and neuropathy (n = 5). The results were compared with those from matched normal control subjects. The diagnoses were based on clinical phenotype as well as histopathologic and molecular analysis.

RESULTS

Cerebral glucose uptake was impaired in all patients, both with and without CNS symptoms, particularly in the occipital and temporal lobes. The vasoreactivity of the small arterioles to acetazolamide did not differ significantly between the patients and healthy control subjects or between the different groups of mitochondrial disorders.

CONCLUSIONS

MELAS does not appear to be a functional disturbance of arterioles leading to an ischemic vascular event. The clinical symptoms in MELAS are not the result of a mitochondrial angiopathy but are the consequences of a mitochondrial cytopathy affecting neurons or glia. There is no correlation between the decreased glucose metabolism and the duration of the disease.

SPECT findings in mitochondrial encephalomyopathy

We investigated the alterations in regional cerebral blood flow (rCBF) in mitochondrial encephalomyopathy (MEM), using [123I]N-isopropyl-p-iodoamphetamine (IMP) or 99mTc-hexamethyl propyleneamine oxime SPECT in 10 MEM patients.

METHODS

Four of the patients had MEM with lactic acidosis and strokelike episodes (MELAS), 2 had Kearns-Sayre syndrome (KSS), 1 had myoclonic epilepsy with ragged red fibers (MERRF) and 3 had cytochrome C oxidase deficiency (CCOD). Cerebral perfusion reserve was obtained from 6 patients (3 MELAS, 1 MERRF, 1 KSS, 1 CCOD) for a comparative analysis using the split-dose 123I-IMP SPECT method before and after the injection of acetazolamide.

RESULTS

All patients with MELAS showed focal hypoperfusion in the parietal and/or occipital lobes. Follow-up studies (3 MELAS patients) revealed extension or improvement in the abnormal perfusion. The hypoperfused lesions were correlated with abnormal CT/MRI findings. Perfusion was normal in 1 MERRF, 2 KSS and 3 CCOD patients, whereas CT/MRI findings in 1 MERRF, 1 KSS and 1 CCOD patient were abnormal. The cerebral perfusion reserve in 3 MELAS patients was decreased significantly compared with that in patients with other types of MEM (MELAS 7.4%, other MEM 33.8%; p < 0.05).

CONCLUSION

The rCBF was altered specifically in patients with MELAS, suggesting that brain perfusion SPECT will be useful in diagnosing and assessing such patients. The decreased cerebral perfusion reserve in patients with MELAS may represent an important feature of the pathogenesis of the strokelike episodes. The SPECT findings of patients with other types of MEM (MERRF, KSS and CCOD) were normal.

[Clinical usefulness of myocardial iodine-123-15-(p-iodophenyl)-3(R,S)-methyl-pentadecanoic acid distribution abnormality in patients with mitochondrial encephalomyopathy based on normal data file in bull's-eye polar map]

Visual interpretation of iodine-123-beta-15-(p-iodophenyl)-3(R,S)-methyl-pentadecanoic acid (123I-BMIPP) myocardial images cannot easily detect mild reduction in tracer uptake. Objective assessment of myocardial 123I-BMIPP maldistributions at rest was attempted using a bull's-eye map and its normal data file for detecting myocardial damage in patients with mitochondrial encephalomyopathy. Six patients, two with Kearns-Sayre syndrome and four with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and 10 normal subjects were studied. Fractional myocardial uptake of 123I-BMIPP was also measured by dynamic static imaging to assess the global myocardial free fatty acid. These data were compared with the cardiothoracic ratio measured by chest radiography and left ventricular ejection fraction assessed by echocardiography. Abnormal cardiothoracic ratio and lower ejection fraction were detected in only one patient with Kearns-Sayre syndrome. Abnormal fractional myocardial uptake was detected in two patients (1.61%, 1.91%), whereas abnormal regional 123I-BMIPP uptake assessed by the bull's-eye map was detected in five patients (83%). All patients showed abnormal uptake in the anterior portion, and one showed progressive atrioventricular conduction abnormality and systolic dysfunction with extended 123I-BMIPP abnormal uptake. The results suggest that assessment based on the normal data file in a bull's-eye polar map is clinically useful for detection of myocardial damage in patients with mitochondrial encephalomyopathy.

Cerebral oxygen and glucose metabolism and blood flow in mitochondrial encephalomyopathy: a PET study

Cerebral blood flow (CBF), oxygen metabolism (CMRO2), and glucose metabolism (CMRGlc) were measured using positron emission tomography in five patients diagnosed as having mitochondrial encephalomyopathy. The molar ratio between the oxygen and glucose consumptions was reduced diffusely, as CMRO2 was markedly decreased and CMRGlc was slightly reduced. The CBF showed less changes. The CBF increase on hypercapnia was smaller than normal, though this was not significant. CBF with hypocapnia demonstrated a significant reduction compared with the normal. These results suggest that oxidative metabolism is impaired and anaerobic glycolysis relatively stimulated, due to a primary defect of mitochondrial function, and that mild lactic acidosis occurs in brain tissue because of impaired utilisation of pyruvate in the TCA cycle. As these findings appear to indicate directly a characteristic of this disease, such measurements may be a useful tool for assessment of the pathophysiology and for diagnosis of mitochondrial encephalomyopathy.

99mTc-HMPAO brain single photon emission computerized tomography in mitochondrial encephalomyopathies

BACKGROUND

Mitochondrial encephalomyopathies are heterogeneous diseases with common clinical features of muscle and/or the central nervous system. Although molecular and histological diagnoses have been established, imaging modalities for the functioning evaluation of these patients are still obscure. In this study, we tried to use 99mTc-HMPAO brain SPECT images to analyze various mitochondrial encephalomyopathies.

METHODS

We examined 99mTc-HMPAO Brain SPECT studies of 15 patients with various types of mitochondrial encephalomyopathy (3 Leber's hereditary optic neuropathy (LHON), 4 Kearns-Sayre syndrome (KSS), 4 mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), 3 myoclonic epilepsy and ragged-red fiber disease (MERRF), and 1 Leigh syndrome), diagnosed by molecular studies.

RESULTS

The results of our studies show obviously decreased radiotracer accumulation in the parieto-temporal regions after stroke-like episodes in patients with MELAS and MERRF: Relatively diminished brain perfusion in patients with KSS is noted, probably secondary to severe encephalomyopathy or subdural effusion. However, there seems to be no significant correlation between the clinical manifestations and the imaging findings in LHON and Leigh.

CONCLUSIONS

99mTc-HMPAO Brain SPECT is useful in the diagnosing and assessment of the progress of MERRF, MELAS and KSS. However, its role in LHON and Leigh syndrome seems to be debatable.

123I-IMP SPECT findings in mitochondrial encephalomyopathies

We performed N-isopropyl-[123I]p-iodoamphetamine (IMP) single photon emission computed tomography (SPECT) in three patients with Leigh syndrome, two patients with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and two siblings with progressive external ophthalmoplegia (PEO). The SPECT images were compared with the findings on magnetic resonance imaging (MRI) and computed tomography (CT). All Leigh syndrome patients showed low accumulation areas (LAA) bilaterally in the frontal lobes and the basal ganglia. The frontal lobe LAA was seen even in an area without abnormalities on CT/MRI. Each MELAS patient showed a focal LAA. SPECT could also detect an old stroke-like lesion that was no longer shown by CT/MRI. However, SPECT did not show LAA in the basal ganglia, which showed calcification on CT or abnormal signal intensity on MRI. MRI in the 2 PEO patients showed lesions bilaterally in the basal ganglia in one, and in the internal capsules in the other. SPECT showed LAA not only in corresponding areas, but also in the occipital lobes, where no lesions were revealed by MRI. Thus, 123I-IMP SPECT was more sensitive than CT/MRI for detecting stroke-like lesions in MELAS patients, although it did not detect small lesions in the basal ganglia. LAA in the frontal lobes and occipital lobes may be SPECT findings characteristic of Leigh syndrome and PEO, respectively.

Mitochondrial encephalomyopathies: CT and MRI findings and correlations with clinical features

Seven patients (3 men, 4 women; age 15-48 years) from 6 families with mitochondrial encephalomyopathies were studied. There were 4 patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and 3 patients with myoclonus epilepsy and ragged-red fibers (MERRF). The clinical course was variable in both MELAS and MERRF patients. Interestingly, one MERRF patient had putaminal hemorrhage with left hemiplegia. In MELAS patients, brain computed tomography (CT) revealed cerebral hypodensity lesions affecting all four lobes and relative sparing of the basal ganglia and the thalamus. The CT of MERRF patients showed cerebral and cerebellar cortical atrophies in two and ventricular dilatation in one. During the recovery stages, magnetic resonance images (MRI) revealed subcortical white matter lesions in two MELAS patients and one MERRF patient. These subcortical white matter lesions were most prominent in the paraventricular areas. The present data indicate that in MELAS the hypodense lesions tend to affect the cerebral hemisphere and to spare the subcortical gray matter. Furthermore, the involvement of the paraventricular white matter may occur in both MELAS and MERRF.

Familial mitochondrial encephalopathy with fetal ultrasonographic ventriculomegaly and intracerebral calcifications

In two sibs antenatal ultrasonography revealed identical intracranial calcification, ventricular widening and microcephaly. The first pregnancy was artificially terminated at 19 weeks. Post-mortem examination of the brain revealed destructive calcification and extracerebral neuronal heterotopia. The second sib went to term but died 48 h after birth from irreversible lactic acidosis. Autopsy showed extensive encephalopathy with cavitation and calcification in the cerebral hemispheres, polymicrogyria, multiple neuronal heterotopia, partial callosal dysgenesis, and severe Leigh syndrome, together forming a continuum of early and late brain disruption. Mitochondrial respiratory chain abnormalities, mainly affecting complexes I and IV, and deficiency of pyruvate dehydrogenase complex were detected in skeletal muscle and in liver. A normal functioning of the respiratory chain was found in the fibroblasts. Analysis of mtDNA from muscle, liver and blood revealed normal amounts of intact mtDNA without any of the known point mutations associated with MELAS, MERRF or Leigh syndromes. The early fetal disruption and necrotic changes in the brains of sibs indicate a specific genetically determined disorder which affects neuronal migration, a finding not previously associated with respiratory chain disorders. The present disorder may mimic antenatal congenital infectious encephalopathy because of the combined finding of microcephaly and destructive intracerebral calcification.

Mitochondrial encephalomyopathy: variable clinical expression within a single kindred

The clinical manifestations of mitochondrial encephalomyopathy are described in four generations of a single kindred. The age of onset of major neurological disturbance varied from 3-70 years. In some patients, deafness was the only manifestation; in others, recurrent bouts of status epilepticus associated with focal neurological deficits and headache, caused severe disability or death. Examples of all three adult forms of mitochondrial encephalomyopathy: MELAS, MERFF and Kearns Sayre syndrome, were represented within the kindred. Associated features included deafness, short stature, non-insulin-dependent diabetes mellitus, migraine, peptic ulceration and severe constipation. The nt 3243 A-G MELAS mutation was detected in two members of the kindred. This study highlights the diversity of clinical expression of a mitochondrial mutation within a single kindred.

Mitochondrial dysfunction in Rett syndrome. An ultrastructural and biochemical study

We report the ultrastructural and biochemical alterations of muscle mitochondria in two girls with Rett syndrome. Our findings suggest the presence of an energy metabolism impairment the primary or secondary role of which in the pathogenesis of this syndrome cannot be defined at present.

Mitochondrial disorders: analysis of their clinical and imaging characteristics

PURPOSE

Investigation of the clinical, imaging, and in vivo MR spectroscopy (MRS) characteristics of disorders of mitochondrial function.

METHODS

Clinical, imaging (five CT and 20 MR examinations), and MRS (six studies in five patients) findings in 19 patients with mitochondrial disorders were retrospectively reviewed. Results were critically analyzed and, when applicable, compared with results in the literature.

RESULTS

Patients included four with mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), two with myoclonus, epilepsy, and ragged red fibers (MERRF), two with Kearns-Sayre syndrome, seven with Leigh syndrome, one with progressive cerebral poliodystrophy (Alpers syndrome), and three with trichopoliodystrophy (Menkes disease). MELAS, MERRF, and Kearns-Sayre tended to occur in older children and adults, whereas Leigh syndrome, Alpers syndrome, and Menkes disease occurred in infants and young children. All diseases involved gray matter early in their course, manifest primarily as T2 prolongation, with the deep cerebral nuclei being involved more often than the cerebral cortex. When T2 prolongation was seen in the white matter (MELAS, MERRF, Kearns-Sayre, Leigh), the peripheral and retrotrigonal white matter showed early involvement. Patients with Menkes disease showed rapidly progressive atrophy accompanied by large subdural hematomas. Proton MRS showed an elevated lactate level in involved regions of the brain; the lactate peak disappeared in old areas of T2 prolongation.

CONCLUSIONS

Mitochondrial disorders have a wide range of both clinical and imaging findings. Although no one set of findings is diagnostic of these disorders, the combination of deep gray matter involvement and peripheral white matter involvement in young adults or children should suggest the diagnosis, especially when associated with an elevated lactate level on proton MRS.