Differential Diagnosis for Unilateral Hemiplegia without MRI Findings

Single Most Likely Diagnosis

• Functional Hemiplegia: This condition, also known as conversion disorder or functional neurological symptom disorder, presents with neurological symptoms that cannot be explained by medical conditions. It is a common cause of unexplained neurological symptoms, including hemiplegia, especially when imaging studies like MRI are normal.

Other Likely Diagnoses

• Early Ischemic Stroke: In the early stages of an ischemic stroke, MRI findings might not be apparent, especially if the scan is done very soon after symptom onset. The lack of findings on MRI does not rule out an ischemic stroke, as diffusion-weighted imaging (DWI) changes may take time to develop.
• Seizure or Postictal State: A seizure can cause transient hemiplegia, and the postictal state (after a seizure) can manifest with focal neurological deficits, including hemiplegia. MRI might not show any abnormalities if the seizure was not due to a structural lesion.
• Migraine with Aura: Some migraines can present with aura symptoms that include hemiplegia. These symptoms are usually transient but can be quite alarming.

Do Not Miss Diagnoses

• Cervical Artery Dissection: Although less common, dissections of the cervical arteries (carotid or vertebral) can lead to stroke. Early MRI might not show the dissection or the resulting ischemia clearly, making clinical suspicion crucial.
• Venous Sinus Thrombosis: This condition can cause stroke and might not be visible on standard MRI sequences unless specific venous imaging is performed.
• Intracranial Vasculitis: Vasculitis affecting the intracranial vessels can cause stroke and might not be evident on initial MRI scans, requiring further investigation like angiography.

Rare Diagnoses

• Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS): A rare mitochondrial disorder that can cause stroke-like episodes, which might not always have corresponding lesions on MRI.
• Susac Syndrome: A rare condition characterized by microangiopathic changes in the brain, retina, and cochlea, which can present with stroke-like symptoms and might have subtle or no findings on MRI.
• Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, which can cause neurological symptoms, including stroke-like episodes, without clear findings on MRI.