Differential Diagnosis for Positive c-ANCA with Negative PR3 Antibody in Patient with 3rd Cranial Nerve Palsy
- Single Most Likely Diagnosis
- Microscopic Polyangiitis (MPA): Although c-ANCA is more commonly associated with Granulomatosis with Polyangiitis (GPA), a negative PR3 antibody and the presence of 3rd cranial nerve palsy could still suggest MPA, especially if there are other systemic symptoms such as renal involvement or pulmonary symptoms. MPA can occasionally be c-ANCA positive, especially in the absence of PR3 antibodies.
- Other Likely Diagnoses
- Granulomatosis with Polyangiitis (GPA) with atypical antibody profile: Despite the negative PR3 antibody, GPA should still be considered, especially with cranial nerve involvement, which can occur in GPA. Some patients with GPA may have a negative PR3 antibody but positive c-ANCA due to the presence of other autoantibodies.
- Eosinophilic Granulomatosis with Polyangiitis (EGPA): Although more commonly associated with p-ANCA, EGPA can occasionally present with c-ANCA positivity. The presence of asthma, eosinophilia, and other systemic symptoms would support this diagnosis.
- Do Not Miss Diagnoses
- Tolosa-Hunt Syndrome: This is a rare disorder characterized by painful ophthalmoplegia due to nonspecific inflammation of the cavernous sinus or superior orbital fissure. It can mimic the cranial nerve palsy seen in vasculitic conditions and is important to consider due to its responsiveness to corticosteroids.
- Infectious Causes (e.g., Tuberculosis, Syphilis): These can cause cranial nerve palsies and may have associated positive ANCA tests due to the chronic inflammatory nature of the infections. Missing these diagnoses could lead to significant morbidity or mortality.
- Rare Diagnoses
- Primary Central Nervous System Vasculitis: This condition involves inflammation of the blood vessels in the brain and spinal cord and can present with a variety of neurological symptoms, including cranial nerve palsies. It is rare and diagnosis often requires a combination of clinical presentation, imaging, and sometimes biopsy.
- ANCA-associated vasculitis with unusual organ involvement: Some patients with ANCA-associated vasculitis may present with atypical organ involvement or unusual antibody profiles, making diagnosis challenging. A high index of suspicion and thorough investigation are necessary in these cases.