Differential Diagnosis for 3rd Cranial Nerve Paralysis with Positive C-ANCA and Negative PR3 and MPO

• Single Most Likely Diagnosis

  • Granulomatosis with Polyangiitis (GPA): This condition, formerly known as Wegener's granulomatosis, is a form of vasculitis that affects small- and medium-sized vessels. The presence of positive C-ANCA (cytoplasmic antineutrophil cytoplasmic antibodies) with negative PR3 (proteinase 3) and MPO (myeloperoxidase) is highly suggestive of GPA, especially when combined with symptoms like 3rd cranial nerve paralysis, which can occur due to the inflammatory nature of the disease affecting various parts of the body, including the nervous system.

• Other Likely Diagnoses

  • Microscopic Polyangiitis (MPA): Although MPA is more commonly associated with P-ANCA (perinuclear antineutrophil cytoplasmic antibodies) and positive MPO, some cases can present with C-ANCA positivity. The clinical presentation can include neurological manifestations due to vasculitis.
  • Eosinophilic Granulomatosis with Polyangiitis (EGPA): Formerly known as Churg-Strauss syndrome, EGPA is another form of vasculitis that can present with positive ANCA (either C-ANCA or P-ANCA) and involves various organs, including the nervous system. However, it is typically associated with asthma and eosinophilia.

• Do Not Miss Diagnoses

  • Giant Cell Arteritis (GCA): Although GCA is not typically associated with ANCA positivity, it can cause cranial nerve palsies, including 3rd nerve paralysis, due to inflammation of the arteries supplying the nerves. Missing this diagnosis could lead to serious complications, including vision loss.
  • Pituitary Apoplexy: This condition involves sudden hemorrhage or infarction of the pituitary gland and can present with acute onset of 3rd cranial nerve paralysis among other symptoms. It is a medical emergency requiring prompt intervention.

• Rare Diagnoses

  • Primary Central Nervous System Vasculitis: This is a rare form of vasculitis confined to the central nervous system and can present with a variety of neurological symptoms, including cranial nerve palsies. The ANCA status can vary, and diagnosis often requires a combination of clinical presentation, imaging, and sometimes biopsy.
  • Neurosarcoidosis: Sarcoidosis is a systemic granulomatous disease that can affect any part of the body, including the nervous system. While it can cause cranial nerve palsies, the association with C-ANCA is not typical, making it a less likely but still possible diagnosis in this context.