Differential Diagnosis for Sudden Onset of Limb Weakness

The patient presents with sudden onset of left arm weakness and right leg weakness, which suggests a neurological issue. Given her medical history and laboratory findings, the following differential diagnoses are considered:

• Single most likely diagnosis

  • Stroke (due to Antiphospholipid Syndrome): The presence of moderately positive lupus anticoagulant, a history of previous miscarriage, and the sudden onset of neurological symptoms suggest Antiphospholipid Syndrome (APS) as a possible cause of stroke. APS is known to increase the risk of thrombotic events, including stroke.

• Other Likely diagnoses

  • Multiple Sclerosis: Although less likely given the absence of sensory disturbances, multiple sclerosis (MS) can present with a wide range of neurological symptoms, including limb weakness. The lack of slurred speech and the specific pattern of weakness (left arm and right leg) could suggest a lesion in the spinal cord or brainstem, which is consistent with MS.
  • Spinal Cord Infarction: This could explain the pattern of weakness, especially if the infarction involves the cervical or thoracic spinal cord. However, spinal cord infarctions are less common and might not be as directly linked to the patient's history of positive lupus anticoagulant.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Vertebral Artery Dissection: Although less common, vertebral artery dissection can lead to stroke and presents with sudden onset of neurological symptoms. It is crucial to consider this diagnosis due to its potential for severe consequences if missed.
  • Cervical Spine Injury or Herniated Disk: Acute cervical spine injury or a herniated disk could cause limb weakness and must be considered, especially if there was any trauma or if the patient reports neck pain.

• Rare diagnoses

  • Mitochondrial Myopathies: These are a group of disorders that affect the mitochondria, leading to muscle weakness. While they could potentially cause limb weakness, they are less likely given the acute onset and the specific pattern of weakness.
  • Neurosarcoidosis: Sarcoidosis affecting the nervous system can cause a wide range of symptoms, including limb weakness. However, it is rare and would typically be associated with other systemic symptoms or findings suggestive of sarcoidosis.