T2-low signal intensity in the cortex in multiple system atrophy

Exploring the frequency and clinical background of the "zebra sign" in amyotrophic lateral sclerosis and multiple system atrophy

In amyotrophic lateral sclerosis (ALS), the "zebra sign" in the precentral gyrus on phase difference enhanced magnetic resonance imaging (PADRE) recently has been reported as a possible imaging biomarker for upper motor neuron (UMN) involvement. A previous study has shown that the "zebra sign" allowed us to differentiate patients with ALS from healthy subjects with excellent accuracy. We validated the usefulness of the sign for differentiating patients with ALS from healthy subjects and investigated whether the "zebra sign" can be observed other neurodegenerative disorders with UMN involvement. The "zebra sign" on PADRE was assessed in 26 patients with ALS, 26 with multiple system atrophy (MSA) and 26 healthy controls, and the sign was observed in 50%, 23%, and no subjects, respectively. ALS patients with the "zebra sign" demonstrated a higher UMN burden score than those without the sign. The "zebra sign" on PADRE is not specific to ALS, also present in MSA, but might reflect the degeneration of the UMN within the motor cortex in neurodegenerative disorders.

Iron accumulation in deep cortical layers accounts for MRI signal abnormalities in ALS: correlating 7 tesla MRI and pathology

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by cortical and spinal motor neuron dysfunction. Routine magnetic resonance imaging (MRI) studies have previously shown hypointense signal in the motor cortex on T₂-weighted images in some ALS patients, however, the cause of this finding is unknown. To investigate the utility of this MR signal change as a marker of cortical motor neuron degeneration, signal abnormalities on 3T and 7T MR images of the brain were compared, and pathology was obtained in two ALS patients to determine the origin of the motor cortex hypointensity. Nineteen patients with clinically probable or definite ALS by El Escorial criteria and 19 healthy controls underwent 3T MRI. A 7T MRI scan was carried out on five ALS patients who had motor cortex hypointensity on the 3T FLAIR sequence and on three healthy controls. Postmortem 7T MRI of the brain was performed in one ALS patient and histological studies of the brains and spinal cords were obtained post-mortem in two patients. The motor cortex hypointensity on 3T FLAIR images was present in greater frequency in ALS patients. Increased hypointensity correlated with greater severity of upper motor neuron impairment. Analysis of 7T T₂^*-weighted gradient echo imaging localized the signal alteration to the deeper layers of the motor cortex in both ALS patients. Pathological studies showed increased iron accumulation in microglial cells in areas corresponding to the location of the signal changes on the 3T and 7T MRI of the motor cortex. These findings indicate that the motor cortex hypointensity on 3T MRI FLAIR images in ALS is due to increased iron accumulation by microglia.

Magnetic resonance imaging reveals neuronal degeneration in the brainstem of the superoxide dismutase 1G93A G1H transgenic mouse model of amyotrophic lateral sclerosis

Magnetic resonance imaging (MRI) is becoming the preferred neuroimaging modality for the diagnosis of human amyotrophic lateral sclerosis (ALS). A useful animal model of ALS is the superoxide dismutase 1G93A G1H transgenic mouse, which shows many of the clinico-pathological features of the human condition. We have employed a 4.7-Tesla MRI instrument to determine whether a noninvasive imaging approach can reveal pathological changes in the nervous system of this animal model. Our T2-weighted MRI revealed consistent changes in brain and brainstem of these mice. Hyperintensities, indicative of neuropathology, were observed in several areas including the nucleus ambiguus, facial nucleus, trigeminal motor nucleus, rostroventrolateral reticular nucleus, lateral paragigantocellular nucleus and the substantia nigra. Histology analysis including neuronal counts of the imaged brains confirmed the T2-weighted MRI findings. Enlarged ventricles and hypointense striations, indicative of global atrophy, were also observed in the brain and cerebellum. This atrophy was confirmed by fresh brain weight data. The extensive global degeneration involving multiple structures suggests a multisystem disease that is similar to human ALS.