Differential Diagnosis for 50yo Man with Left Hemibody Weakness and Normal MRI Brain and Cervelical Spine

• Single Most Likely Diagnosis
  • Stroke or Transient Ischemic Attack (TIA) in a region not visible on MRI: Despite a normal MRI, the clinical presentation of left hemibody weakness is highly suggestive of a vascular event. Small vessel disease or lacunar strokes might not always be visible on standard MRI sequences, especially if the imaging was done after the acute phase.
• Other Likely Diagnoses
  • Multiple Sclerosis (MS): Although MS typically presents with more disseminated lesions in time and space, a clinically isolated syndrome (CIS) could manifest as hemibody weakness. Normal MRI does not rule out MS entirely, as some patients may have minimal or no visible lesions at the time of initial presentation.
  • Spinal Cord Infarction below the level of MRI coverage: If the cervical spine MRI did not cover the entire spinal cord, an infarction in the thoracic or lumbar region could cause hemibody weakness.
  • Peripheral Nerve Disorders (e.g., Brachial Plexopathy): Conditions affecting the brachial plexus or peripheral nerves could lead to weakness, although these typically present with more localized symptoms.
• Do Not Miss Diagnoses
  • Vertebral Artery Dissection or other Vascular Malformations: These conditions can cause stroke or spinal cord infarction and might not be visible on a standard MRI of the brain and cervical spine. They require specific imaging protocols for diagnosis.
  • Cervical Spine or Thoracic Spine Pathology not visible on initial MRI (e.g., epidural abscess, hematoma): Conditions that could compress the spinal cord and cause neurological deficits. Repeat or specialized imaging might be necessary.
  • Intracranial Atherosclerosis: Especially in the setting of risk factors for atherosclerosis, this could lead to stroke and might not be evident on a non-contrast MRI.
• Rare Diagnoses
  • Mitochondrial Disorders (e.g., MELAS Syndrome): These can present with stroke-like episodes and might not have visible lesions on MRI, especially if the condition is not suspected and specific tests are not performed.
  • Inflammatory or Autoimmune Conditions (e.g., Neuromyelitis Optica Spectrum Disorder): Although less common, these conditions can cause significant neurological deficits and might have a normal or non-specific appearance on initial MRI.
  • Paraneoplastic Syndromes: Rarely, these can present with neurological symptoms, including hemibody weakness, due to an immune response to a cancer elsewhere in the body.