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A man in his 70s presented to hospital with type 2 respiratory failure following 12 months of progressive bulbar dysfunction. Examination revealed tongue fasciculation, brisk jaw jerk, wasting and fasciculation of the left hand muscles, left upper limb spasticity and hyperreflexia. Due to the co-existence of upper and lower motor neurone signs in contiguous body segments, a clinical diagnosis of motor neurone disease (MND) was assumed. MRI was performed with axial T2-weighted and susceptibility-weighted imaging (SWI) sequences demonstrating a bilateral ribbon of low signal along the pre-central gyrus, known as the motor band sign (MBS) (figure 1). Intracranial and spinal appearances were otherwise normal. Initial electromyography (EMG) did not demonstrate sufficient evidence of denervation to satisfy neurophysiological MND diagnostic criteria, but a follow-up study was later confirmatory.
MND is frequently diagnosed late due to its insidious and heterogeneous presentation. Many patients consult multiple health professionals and undergo investigations prior to a neurologist’s assessment.1 The principal role of MRI is to exclude mimics, and while brain and/or spinal MRI is not always essential, it should be performed wherever a plausible alternative neuroanatomical explanation exists.2 This is frequently the case in early-stage or focal disease, and in practice, many patients do undergo MRI. However, standard MRI sequences in MND may also demonstrate abnormalities along the corticospinal tracts or motor cortex (MBS), lending support to diagnostic suspicion, particularly when initial EMG is inconclusive, as in this case.
The MBS has been described in the amyotrophic lateral sclerosis (ALS) and primary lateralising sclerosis variants of MND. It results from an excess of iron within the microglia of the primary motor cortex, which causes distortion of the local magnetic field.3 It is usually seen bilaterally and is best appreciated on axial SWI and gradient echo (GRE) sequences, but may occasionally be seen on T2 and fluid attenuated inversion recovery (FLAIR) sequences. A recent study identified MBS in 5% (7/157) of MND patients with only T2/FLAIR images and in 78% (7/9) of those with SWI images.4 7-Tesla MRI has a higher sensitivity than 3-Tesla imaging5 and has identified a correlation between motor cortex hypointensity and the severity of clinical upper motor neurone impairment.6 7 MBS has been recognised in those with early (King’s College ALS stage I) disease,4 but robust prospective studies are needed to evaluate the prevalence of MBS in different MND subtypes and clinical stages.4 8
The MBS is not 100% specific to MND. The motor cortex has a particularly high iron concentration, and pathological accumulation of iron occurs in several neurodegenerative disorders, including Parkinson’s and Alzheimer’s disease.9 10 However, the clinical phenotype of these disorders is quite distinct from MND, and to the best of our knowledge, the MBS has not been reported in spinal or neuromuscular disorders that more closely mimic MND. The diagnostic accuracy of the MBS is improved when combined with simultaneous detection of corticospinal tract FLAIR hyperintensity. These combined findings have a positive predictive value of 90% and are associated with shorter survival.11
In conclusion, in cases where the clinical diagnosis of MND is challenging or initial EMG studies are inconclusive, identification of the MBS may improve diagnostic confidence. Inclusion of axial SWI/GRE sequences improves the sensitivity of routinely acquired MR brain imaging.
The patient’s and his family’s perspective
Dribbling was the very first symptom, followed by slurred speech, which was noticed by family members during a special occasion. This led to doctors appointments, tests and an MRI scan rule out the possibility of a stroke. The next approach was to change my dad’s life-long epilepsy medication from phenobarbitone (as we were advised that this may have had side effects which may have caused the initial symptoms). However this had no effect on the progression of the symptoms. Speech therapy was also tried, but again, found to have no effect.
Full bulbar paralysis followed, resulting in a complete loss of speech, and eventually prevented my dad from swallowing both food and liquids. Five days before he was due to attend an initial Neurology appointment to conduct an EMG (following all previous attempts of diagnosis by elimination), my dad collapsed, unable to expel the carbon dioxide that had built up in his bloodstream. Rushed to hospital and into resus, an instant ‘Do Not Attempt Rescusitation’ order was applied with no expectation of survival. However, following initial intensive care and transfer to a Critical Care Unit, rehabilitation enabled us to continue to final diagnosis and gave us several more months of valuable time with Dad, during which he could communicate with us by writing, and we could say goodbye.
Even though our intuition knew, we felt the path to diagnosis was too long and frustrated from the outset by a lack of neurological expertise locally. To receive the formal diagnosis ‘Motor Neurone Disease’ was actually a relief following the exhaustion of all diagnostic tests, and from our perspective, the brain scan images showing the motor band sign, helped to provide supportive diagnostic evidence of the devastating condition, where other tests hadn’t. As a family you are living in grief constantly, from diagnosis confirmation to death, and the journey to confirm the diagnosis is just as painful, if not more.
Recognition of the motor band sign (a ribbon of low signal along the pre-central gyrus) can provide a useful radiological clue to the diagnosis of motor neurone disease (MND).
Including iron-sensitive sequences (SWI/GRE) as part of MR imaging protocols markedly improves detection of this sign.
The motor band sign should be used in the right context, when there is a clinical suspicion of MND, and should not be used in isolation.
Patient consent for publication
Contributors DW prepared the first draft and revisions of the manuscript. All authors contributed to the revision of the manuscript and the clinical care of the patient. SD conceived the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.