N-isopropyl-p-[123I]iodoamphetamine SPECT in MELAS syndrome: comparison with CT and MR imaging

A Case of MELAS: Hyperperfused Lesions Detected by Non-invasive Perfusion-weighted MR Imaging

We report a case of MELAS in which lesions were detected by perfusion-weighted MR imaging. Perfusion-weighted MRI using contrast media (PWI) and FAIR (flow-sensitive alternating inversion recovery), an arterial spin labeling method, clearly showed these lesions as hyperperfused areas. One of these lesions, diminished after steroid therapy, could also be detected by FAIR.

Discordance between cerebral oxygen and glucose metabolism, and hemodynamics in a mitochondrial encephalomyopathy, lactic acidosis, and strokelike episode patient

A patient with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episode (MELAS) syndrome underwent serial measurement of cerebral blood flow with xenon computed tomography (Xe-CBF) while presenting with strokelike episodes accompanied by a cerebral lesion. He underwent positron emission tomography (PET) measurement of the regional cerebral blood flow (PET-CBF), metabolic rate of oxygen (CMRO2), and glucose (CMRGlu) after his symptoms and lesion disappeared. During the symptomatic period, Xe-CBF and the Xe-CBF response to acetazolamide loading were well preserved both in and outside the low-density lesion. In the PET study, decreased CMRO2 and increased PET-CBF and CMRGlu were noted in the entire brain. The strokelike episodes of patients with MELAS are more likely attributed to the failure of oxygen metabolism than to a vascular accident.

Functional brain imaging in neuropsychiatric disorders of childhood

This review article presents a summary of the current state-of-the-art of functional brain imaging, with a primary focus on childhood neuropsychiatric disorders. Coverage is emphasized for developments that appear to be of current or potential future importance for the child neurologist and related pediatric specialist, and also from the perspective of the developmental neuroscientist. Emphasis is placed on the modalities of single photon emission computed tomography (SPECT), positron emission tomography (PET), and both "conventional" and "functional" magnetic resonance imaging, (MRI) including reference to the major new radiopharmaceutical and magnetic resonance-based imaging agents and techniques. The fundamental physicochemical processes underlying such studies are outlined, with citation of sources of more detailed information for the interested reader. A variety of imaging studies are reviewed for selected groups of childhood neuropsychiatric disorders, designed to illustrate the achievements and future promise of these imaging modalities. Areas of concentration are suggested for future imaging research in the field of childhood behavioral disorders, where these methods seem critical to improved understanding of pathogenetic mechanisms, as well as development of more effective treatment strategies.

Neuroradiological features of six kindreds with MELAS tRNA(Leu) A2343G point mutation: implications for pathogenesis

OBJECTIVE

To determine the neuroradiological abnormalities associated with subjects carrying the mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) tRNA(Leu)(UUR) A3243G point mutation

METHODS

Mitochondrial genetic analysis was performed on 24 subjects from six kindreds with the MELAS tRNA(Leu)(UUR) A3243G point mutation. Cerebral CT and MRI were performed on 24 patients and 15 patients respectively. Previous neuroradiological investigations including cerebral CT from four deceased members of the families were also reviewed. Histological examination of postmortem specimens of two patients within the kindreds was performed.

RESULTS

The commonest radiological finding was basal ganglia calcification. Other abnormalities included focal lesions and cerebellar and cerebral atrophy. Basal ganglia calcification was progressive, symmetric, and asymptomatic. Histologically, basal ganglia calcification in one patient was found to be in the pericapillary regions of the globus pallidus, with no neuronal involvement. Focal lesions most commonly involved the grey matter of the parietal and occipital lobes and cerebellum. Histopathological examination suggested that these were due to cellular rather than vascular dysfunction. Enlargement of the fourth ventricle was the first sign of cerebellar atrophy. Cerebral and cerebellar atrophy were only present with severe disease.

CONCLUSIONS

These radiological findings, when considered in the context of the clinical and pathological findings, seem to reflect two major disease processes: an intermittent abrupt loss of function associated with cell injury from which there is at least partial recovery and a slowly progressive degenerative process causing basal ganglia calcification, and cerebral and cerebellar atrophy. The clinical and radiological features resulting from these processes are distinctive and provide insight into the consequences of mitochondrial dysfunction on the brain.

Cerebral blood flow and oxygen metabolism before and after a stroke-like episode in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS)

Cerebral blood flow and oxygen metabolism were examined in two patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) using positron emission tomography (PET). Regional cerebral blood flow (rCBF), regional cerebral oxygen metabolic rate (rCMRO2) and regional oxygen extraction fraction (rOEF) were determined with the steady-state technique using oxygen-15-labeled tracers (15O2, C15O2 and C15O). Case 1, a 45-year-old woman, presented with abrupt onset of fluent aphasia. T2-weighted magnetic resonance imaging (MRI) showed a high signal intensity lesion in the left temporoparietal region. The first PET study on day 16 showed increased rCBF and decreased rCMRO2 in the temporal region. In the second PET study, on day 35, rCBF in the temporal region had decreased. Case 2 was a 19-year-old male; the second son of Case 1. He complained of transient blurring of vision, and then generalized tonic-clonic convulsion occurred. A PET study six days before this stroke-like episode demonstrated increased rCBF in both frontal lobes and putamen, where MRI showed lesions after the episode. Focal hyperemia of the lesion antedated and lasted for at least sixteen days after the stroke-like episode in these MELAS patients. These stroke-like episodes appear to be the result of metabolic dysfunction in neural tissue, although the role of an ischemic vascular event cannot be ruled out.

Electrophysiological brainstem dysfunction in a child with Leigh disease

We evaluated brainstem dysfunction in a girl with Leigh disease. Neuroradiological and neurophysiological tests included brain magnetic resonance imaging, [123I]IMP single-photon emission computed tomography (SPECT), auditory brainstem responses (ABRs), short-latency somatosensory evoked potentials (SSEPs), electrically elicited blink reflexes (BRs) and all night polysomnography (PSG). The basal ganglia and midbrain contained areas of low accumulation on [123I]IMP SPECT images. Serial analysis of ABRs and SSEPs showed progressive disturbances of the brainstem wave components. The R2 components of the BRs were impaired. All night PSG revealed disturbances in both the tonic and phasic components of REM sleep. These findings suggested the multimodality tests in combination with neuroradiologic examinations are useful for assessing brainstem dysfunction in patients with Leigh disease.

Mitochondrial encephalopathies

Although no single neurological manifestation is specific of mitochondrial encephalopathies, several neurological syndromes are clearly suggestive of the diagnosis. Muscle biopsy for histochemicals, biochemical, and mitochondrial DNA studies is frequently necessary to establish diagnosis of mitochondrial encephalopathy presenting with such neurological syndromes. Mitochondrial encephalopathies most frequently result from nuclear gene defects and biochemical studies are frequently helpful in reaching a specific diagnosis. Various therapeutic interventions are beneficial in selected cases.

The “S” in MELAS

MELAS syndrome is one of several mitochondrial-inherited encephalomyopathies distinguished from the others by its unique stroke-like episodes. A case is presented that illustrates the importance of acknowledging the heteroplasmic nature of this disease when making its diagnosis. The mitochondrial DNA (mtDNA) point mutation characteristic of MELAS was eventually detected by analysis of a muscle biopsy specimen after initial studies of a serum sample were negative for the same genetic defect. Other diagnostic features of MELAS syndrome are described; these include characteristic computed tomography (CT), magnetic resonance imaging (MRI), angiography, single photon emission computed tomography using N-isopropyl-p-[123-I]-Iodoamphetamine (IMP-SPECT), and pathological findings. Finally, various theories regarding the etiology of stroke in MELAS syndrome as well as available treatment options are discussed.

A transcranial doppler ultrasonography study of cerebrovascular CO2 reactivity in mitochondrial encephalomyopathy

BACKGROUND AND PURPOSE

To elucidate the pathogenic role of vascular involvement such as mitochondrial angiopathy in patients with mitochondrial encephalomyopathy (MEM). we used the transcranial Doppler sonography (TCD) method to detect impairment of cerebrovascular CO2 reactivity.

METHODS

The cerebral perfusion reserve in 13 MEM patients, including 6 with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) was studied by TCD for different CO2 partial pressures. For the parameter of mean flow velocity, the mean spatial Doppler frequency (fm) was obtained from the right and left middle cerebral arteries and basilar artery under conditions of normocapnia, hypercapnia, and hypocapnia in cases in which hyperventilation was possible. By fitting the obtained fm and the end-tidal CO2 partial pressure (PETCO2) to the exponential formula fm = a x e(K < PETCO2), where a is the theoretical fm at a PETCO2 of 0 mm Hg, the parameter K, an index of CO2 reactivity, was calculated.

RESULTS

The K value was lower than control values at at least one site of the middle cerebral arteries and basilar artery of all patients with MELAS as well as the other MEM patients except for one patient with myoclonic epilepsy with ragged-red fiber and one with Kearns-Sayer syndrome.

CONCLUSIONS

Our results suggest that there is a high incidence of impairment of cerebrovascular CO2 reactivity in MEM patients. Moreover, the noninvasive TCD method was found useful for evaluation of cerebral hemodynamics in MEM patients.

Study on the primary visual cortex of visually impaired subjects by means of 123I-IMP SPECT and MRI

We conducted a study of rCBF in the primary visual cortex of visually impaired subjects who have not been subjected to external stimulation for a long period, by means of 123I-IMP SPECT and MRI. The four subjects had lost their sight due to brain tumors (n = 2), glaucoma (n = 1) and trauma (n = 1). 123I-IMP SPECT showed no differences between the visually impaired group and a visually sound control group on visual analysis as well as semiquantitative analysis. MRI of the visually impaired subjects showed no organic changes, such as atrophy, in the occipital cortex. In conclusion, visually impaired subjects have no decrease in rCBF and no anatomical changes in the primary visual cortex.

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.

Cerebral hyperemia in MELAS

BACKGROUND

The pathophysiology of stroke-like episodes in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) is uncertain.

CASE DESCRIPTION

We studied a 24-year-old man with MELAS who had fluent aphasia and right hemianopia. Magnetic resonance imaging and computed tomography showed a large infarction in the parietal, temporal, and occipital lobes. We performed serial planar 133Xe regional cerebral blood flow studies and single-photon emission computed tomography. Fifteen and 26 days after the stroke-like episode, there was generalized hyperperfusion, highest in infarcted areas. Four and 8 months after the stroke-like episode, the brain was still hyperemic, with highest flow in noninfarcted tissue. Reactivity to CO2 was less than normal within the infarct at 26 days but improved thereafter. In the noninfarcted region, vasomotor reactivity was impared at 4 months, when resting flows were at their peak.

CONCLUSIONS

We observed generalized cerebral hyperemia and fluctuating CO2 reactivity in MELAS, possibly a consequence of local lactic acid production. In addition, this case suggests that nonquantitative functional imaging may be misleading in MELAS.

Adrenoleukodystrophy: cortical hypoperfusion demonstrated with 99mTc-HMPAO SPECT

Regional cerebral blood flow was investigated in an 8-year-old boy with adrenoleukodystrophy by single photon emission computed tomography. The use of 99mTc-hexamethylpropylene amine oxime revealed markedly reduced blood flow in the occipital, parietal, and temporal cortical gray matter, in addition to the anticipated reduction in white matter. The area with a decreased blood flow was more extensive than that detected by x-ray computed tomography.

Electrophysiological and 99mTc-HMPAO-SPECT studies in Menkes disease

A diagnosis of Menkes kinky hair disease was made in two brothers who had typical clinical symptoms and laboratory findings. The older one, 11 months old at the time of diagnosis, showed an EEG pattern of low amplitude and slow waves. Visual evoked potentials (VEPs) were absent, brainstem auditory evoked potentials (BAEPs) were abnormal. Regional cerebral blood flow (rCBF) studied by hexamethylpropyleneamine oxime single photon emission computed tomography (99mTc-HMPAO-SPECT) revealed reduced blood flow in both frontal and the right temporal regions. The younger boy, followed from birth, started seizures at the age of 3 months and had a hypsarrhythmia-like EEG. BAEPs were abnormal with prolongation of the latencies at the age of 12 months, while VEPs were near normal at 6 months, but disappeared by the age of 18 months. 99mTc-HMPAO-SPECT revealed an unexpected left parietal hyperperfusion.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS): current concepts

Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome is one of many mitochondrially inherited multisystem diseases. The features of 110 reported mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes patients are reviewed to define the clinical spectrum of this disease. The clinical disorder, in addition to emerging concepts of genetic etiology, is promoting our understanding of mitochondrial functions. New knowledge may lead to more rational therapies. Finally, the recent revolution in the study of mitochondrial diseases may further our understanding of other degenerative disorders and even aging.

Brain single-photon emission computed tomography for behavior disorders in children

Single-photon emission computed tomography (SPECT) of the brain has been used to define functional abnormalities in two groups of childhood behavior disorders: (1) a "primary" category in which there is exclusive or predominant presentation with cognitive and/or behavioral dysfunction and (2) encephalopathies, often defined etiologically at the biochemical or molecular level, in which clinical expression includes, but is not confined to, neural dysfunction. Radiopharmaceuticals available for such studies are manifold, but those used to date have been predominantly perfusion agents, eg, Xenon-133 (133Xe) and technetium-99m (99mTc) hexamethylpropylene amine oxime, and studies with [99mTc]bicisate are eagerly awaited. Xenon-133 studies require that the patient be in the field of view of the detector while the tracer is administered. This renders it difficult for a subject to perform cognitive and other exercises while being imaged, because the environment is quite foreign. On the other hand, the 99mTc-labeled perfusion agents permit a scintigraphic "snapshot" of regional cerebral blood flow during a behavioral event without having to have the patient under the imaging instrument. Thus, one can separate the administration of the radiotracer, which can be done under more controlled and physiological conditions, from the actual imaging. In addition, greater spatial resolution is achieved with the technetium-based agents. Currently, multidetector or dedicated annular crystal-type cameras are the preferred brain SPECT devices, and they are essential to applications such as cortical "activation mapping" or tomographic detection of receptor systems. Close attention to technical detail and standardization of the child's behavioral environment during the investigation are critical to a successful study. The relative advantages and disadvantages of qualitative versus semiquantitative analysis of imaging date are reviewed. Among primary behavioral disorders, 133Xe SPECT studies in attention deficit disorder-hyperactivity (ADHD) have suggested a pattern of hypoperfusion of striatal and periventricular structures with sensorimotor cortical hyperperfusion. This pattern is consistent with some neurophysiological models of the disorder. In cerebral palsy, perfusional abnormalities have paralleled clinical deficits and may offer information to help predict outcome. The important field of childhood affective disorders (schizophrenia, juvenile autism, depression, etc) remains largely unstudied with SPECT. Finally, representative examples of the use of SPECT to study perfusion in encephalopathies with behavioral expression (phenylketonuria, MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes) syndrome, Wilson's disease, etc) are given.

Mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS): clinical, radiological, pathological, and genetic observations

We reviewed 10 patients (5 males, 5 females) with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. The age of symptom onset ranged from 3 months to 12 years. All had lactic acidosis, multiple stroke-like events with secondary neurological deficits, radiological changes of progressive brain infarction, and muscle biopsy showing ragged-red fibers. In patients with earlier onset of symptoms (< 2 yr), involvement tended to be more diffuse, with failure to thrive and early onset of delayed development. Patients whose symptoms appeared later tended to have focal neurological deficits with migraine-like headache, and a rate of cognitive regression reflecting the rapidity of disease progression. Radiological changes included multiple areas of infarction with initial predilection for parietal occipital areas, progressing to generalized atrophy. Pathological findings in muscle biopsies included type 1 fiber predominance, ragged-red fibers, increased intermyofibrillar lipid deposition, and abnormal mitochondria. Four patients showed mitochondrial DNA tRNA mutation at position 3,243. No difference was noted in clinical, radiological, or pathological findings in patients with and without this mutation, suggesting that multiple sites of point mutation may give rise to mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.