Brain MRI abnormalities associated with amyotrophic lateral sclerosis: A case illustration

Abstract

Amyotrophic lateral sclerosis is a progressive neurodegenerative pathology. It involves both upper and lower motor neurons, leading to their degeneration. Lower motor neurons can be detected with an electromyogram, but the detection of upper motor neuron dysfunction may be more accurate using MRI. We present the case of a 64-year-old woman with amyotrophic lateral sclerosis, presenting the motor band sign and the bright tongue sign on MRI.

Introduction

Amyotrophic lateral sclerosis (ALS) is an uncommon neurodegenerative pathology. It involves the motor neurons of the corticospinal path and the spinal cord. The clinical manifestations are well portrayed, but the imaging characteristics are not specific [1]. The purpose of this case report is to present the imaging features that may be found in patients with ALS.

Case report

A 64-year-old woman with no known comorbidities presented with a 2-year history of progressive dysarthria, swallowing problems, and weakness of the left hand extending to the contralateral member, consistent with bulbar lateral amyotrophic sclerosis. On examination, she had left-hand muscle atrophy associated with fasciculation with split hand syndrome and pyramidal syndrome in both arms and both legs. Nerve conduction studies and needle electromyography showed evidence of diffuse lower motor neuron signs in 3 regions (bulbar, cervical, and lumbosacral). Based on clinical and EMG (Electromyography) findings the diagnosis of ALS was made. Her brain MRI revealed bilateral hypointensities in the precentral gyrus on susceptibility-weighted imaging, consistent with the motor band sign (Fig. 1). T1 imaging showed an increased signal of the tongue musculature known as the bright tongue sign (Fig. 2). There was no evidence of corticospinal degeneration on the MRI.

Fig. 1.

Susceptibility-weighted imaging revealing bilateral hypointensity in the precentral gyrus secondary to hemosiderin deposition (arrows). Adjacent gyri did not show this sign.

Fig. 2.

The sagittal non-fat-saturated T1 image shows the increased signal of the tongue (arrow) giving a “bright tongue” appearance (A), fat-saturated T1 image shows suppression of the fat's high signal (arrow) (B). Image (C) is a T1 sagittal image demonstrating the normal signal of the tongue of an age-matched normal individual.

Discussion

ALS is a progressive neurodegenerative pathology. It affects upper and lower motor neurons (UMN and LMN), leading to their dysfunction [2]. We distinguish between primary lateral sclerosis secondary to degeneration of the pyramidal tracts and the bulbar form, characterized by initial speech problems, swallowing problems, and progressive muscular atrophy with pure LMN degeneration [[2], [3]–4].

The diagnosis of ALS requires the detection of UMN and LMN degeneration. LMN degeneration can be successfully discerned using electromyography, but susceptibility-weighted imaging (SWI) may be more effective in detecting UMN involvement [4]. The increased T2 signal along the corticospinal tracts’ path could be a sign of corticospinal degeneration, but this finding might be due to normal aging and thus not specific or sensitive to ALS. In our case, the patient didn't show any abnormal signal along the corticospinal tract.

On SWI, the central sulcus must be well observed. The superficial siderosis that results from the accumulation of intracellular iron following microglial phagocytosis of degenerated neurons is what causes the low signal to be present in this area called the motor band sign [5]. It has a band-like configuration along the gray matter of the motor cortex and is easily detected in SWI due to its high resolution [4]. In our patient, this sign was detected bilaterally, explaining the bilateral spasticity.

The low T2 signal is frequently noticed in other diverse neurological pathologies (Alzheimer’s disease, Parkinson's disease, and multiple cerebral infarctions) as well as in older patients, and thereby is not specific to ALS. However, the involvement of the motor cortex in this specific pattern can be a sign of UMN involvement in ALS. Nevertheless, these features can be variably manifested in patients. They depend on the illness's evolution and the importance of UMN involvement [4].

Another sign of ALS is the increased signal of the tongue musculatures on T1-weighted images with suppression on the fat-saturated T1 images, called the “bright tongue sign.” The increased signal is explained by the fatty replacement of the tongue musculature secondary to chronic denervation and is a marker of bulbar involvement in ALS [6]. Other pathologies that may involve the tongue muscles can also exhibit this radiological sign, such as Pompe disease and Kennedy disease [7].

Conclusion

The diagnosis of ALS depends on clinical manifestation and EMG, but MRI may help identify supporting features. A careful analysis of susceptibility-weighted imaging should be performed, searching for an abnormally hypointense T2 signal in the precentral gyrus. The bright tongue sign, if present, indicates chronic denervation. Both of these signs are not specific but are useful if found in clinically suspected patients with ALS.

Patient consent

Written informed patient consent for publication has been obtained.