Sunday, 18 August 2019

Amyotrophic Lateral Sclerosis MRI

Clinical Details  : 45 yo male, from last five months has been having slowly progressive right distal arm, hand and recently right leg weakness which seems to be progressive. There is no sensory symptoms. No bowel bladder disturbance. Recently has also noted some slurrring of speech and tremulousness of both hands. Clinical examination shows poly myoclonus. Hyper reflexia, right plantar is extensor. Mild right facial weakness, eye movements are normal. Sensations are normal.

Clinically suspected Amyotrophic Lateral Sclerosis.
MRI Findings:
Contiguous bilateral symmetric T2 hyperintensity along posterior limb of internal capsule, extending in adjacent Corona radiata and along cortical spinal tract portion of Brainstem.
MRI DWI images normal.
Normal MR Angiography of Brain.
Finding consistent with clinical diagnosis of Amyotrophic Lateral Sclerosis.

Amyotrophic Lateral Sclerosis 

Lou Gehring disease, A motor neuron disease.

Can be defined as a selective degeneration of somatic motor neurons of Brainstem, spinal cord that is lower motor neuron, pyramidal neurons of motor cortex that is upper motor neuron and eventual loss of corticospinal tract fibres.

Diagnostic clue on imaging is bilateral symmetric contiguous long segment T2 hyperintensity extending along corticospinal tract from motor cortex at Precentral gyrus through bilateral corona radiata, posterior limb of internal capsule, Brainstem and onwards.

Imaging differential diagnosis is Distal Wallerian degeneration in which signal abnormality is often unilateral, associated with primary lesion like bleed or infarct if bilateral has to be asymmetric.
Other conditions with T2 hyperintense lesion at various levels of corticospinal tract are metabolic like x linked adrenoleukodystrophy, Wilsons disease, hypoglycaemic comma, demylinating and inflammatory diseases like multiple sclerosis, ADEM, Behcets disease.

Please make one important note that corticospinal tract can appear hyperintense on 3 Tesla MRI due to Fractional anisotrophy related artefacts in a normal fully demylinating brain at any age and mimic Amyotrophic lateral sclerosis. So clinical back up is important before giving the diagnosis solely based on imaging.

Majority of cases are sporadic but in 15 to 20% of cases they are familial. Common in 4th to 7th decade of life. Twice common in males.
Clinically upper motor signs like Babinski sign, spasticity, hyperreflexia andd lower motor neuron signs like asymmetric muscle weakness, atrophy, fasciculation, Hyporeflexia should be looked for. 

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