Unilateral Motor Band Sign in Hemiplegic Primary Lateral Sclerosis

A 68-year-old woman presented with progressive stiffness and weakness of the left upper and lower limbs for three years. There were no sensory disturbances, involuntary movements, wasting or fasciculations of the limbs, bowel or bladder symptoms, or cognitive symptoms. Examination revealed Grade 3 spasticity in the left upper and lower limbs with exaggerated reflexes on the left side. The plantar reflex was extensor on the left and flexor on the right. There was no wasting, loss of cortical sensation, or apraxia. Detailed mental status examination was normal. MRI brain [Figure 1] showed a linear hypointensity in the central sulcus on the right side (motor band sign) with subtle atrophy of the right perirolandic cortex. ASL (arterial spin labelling) images were normal. Nerve conduction studies and electromyography were normal. Cerebrospinal fluid analysis showed no cells with normal sugar and protein levels. A diagnosis of hemiplegic variant of primary lateral sclerosis (Mill's syndrome) was made. She was treated with baclofen and botulinum toxin injection to the left upper limb, with partial symptomatic improvement.Figure 1: (a) Susceptibility-weighted axial image of the brain showing a linear hypointensity in the right primary motor cortex (unilateral motor band sign), (b) FLAIR axial images of the brain showing atrophy of the right perirolandic cortexPrimary lateral sclerosis is a neurodegenerative disorder of the upper motor neurons characterized by UMN symptoms and signs in two of three areas (bulbar, upper limb, and lower limb) without any lower motor neuron involvement for at least 2 years.[1] Mill's syndrome (hemiplegic variant of primary lateral sclerosis) is believed to occur due to unilateral pyramidal tract degeneration and is now considered to be part of the motor neuron disease spectrum. Contralateral midbrain atrophy and ipsilateral cervical spinal cord hyperintensity have been previously reported in this condition.[2,3] A recent case report has highlighted contralateral hemispheric ASL hypometabolism and hemispheric atrophy in a case of Mill's syndrome.[4] A bilateral motor band sign, thought to occur due to iron deposition in the central sulcus, has been reported in classical cases of amyotrophic lateral sclerosis.[5] Motor band sign has a relatively lower sensitivity (around 60%), but a high specificity (over 90%) for differentiating motor neuron disease from its mimics.[6] Less commonly, a bilateral motor band sign has been reported in primary lateral sclerosis as well.[7] The presence of a unilateral motor band sign in Mill's syndrome (hemiplegic primary lateral sclerosis) strengthens the hypothesis that it is a slowly progressive and asymmetrical variant of primary lateral sclerosis. Focal UMN syndromes like Mill's syndrome are often under-recognized early in the disease course. Careful review of brain imaging for biomarkers like a unilateral or bilateral motor band sign, or focal or hemispheric ASL hypoperfusion can be invaluable in making a diagnosis in such cases. Consent Written informed consent was obtained from the patient for the publication of this report. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.