Differential Diagnosis for Sudden Onset of Limb Weakness

The patient's presentation of sudden onset left arm weakness and right leg weakness without sensory disturbances or slurred speech suggests a neurological cause. Given her medical history, current medications, and the results of initial investigations, the following differential diagnoses are considered:

• Single Most Likely Diagnosis

  • Stroke (specifically, a lacunar stroke or a stroke in a non-dominant hemisphere): The sudden onset of weakness in multiple limbs without associated sensory symptoms or speech difficulties could indicate a stroke, particularly one affecting the brainstem or internal capsule where a small lesion can cause significant and localized neurological deficits. The lack of findings on non-contrast CT does not rule out an early or small ischemic stroke.

• Other Likely Diagnoses

  • Multiple Sclerosis (MS): Although less common, MS can present with sudden onset of neurological deficits, including weakness, due to demyelination in the central nervous system. The absence of sensory symptoms does not exclude MS, as presentations can vary widely.
  • Spinal Cord Lesion: A lesion in the spinal cord, such as a tumor, infection, or vascular malformation, could cause bilateral limb weakness, depending on its location and extent. The absence of sensory symptoms might make this less likely, but it remains a consideration.
  • Hemorrhagic Transformation of a Previous Ischemic Stroke: Although the CT is unremarkable, if the patient had a previous stroke that was not diagnosed, there's a possibility of hemorrhagic transformation, which could present with sudden worsening.

• Do Not Miss Diagnoses

  • Brainstem Stroke or Cervicomedullary Junction Pathology: These conditions can present with rapidly evolving neurological deficits, including weakness, and can be life-threatening if not promptly addressed.
  • Spinal Epidural Hematoma or Abscess: These are medical emergencies that can cause sudden neurological deficits, including limb weakness, and require immediate intervention to prevent permanent damage.
  • Pituitary Apoplexy: Although rare, this condition can cause sudden neurological symptoms, including visual disturbances and limb weakness, due to a hemorrhage or infarction of the pituitary gland.

• Rare Diagnoses

  • Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS): A rare mitochondrial disorder that can cause stroke-like episodes, including sudden onset of limb weakness.
  • Susac Syndrome: A rare condition characterized by microangiopathic changes in the brain, retina, and inner ear, which can present with stroke-like episodes and neurological deficits.
  • Cadasil (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy): An inherited condition that affects the blood vessels in the brain, leading to subcortical strokes and dementia, which could present with sudden limb weakness.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and further diagnostic testing to determine the underlying cause of her symptoms.