Pachymeningitis is a very rare disease associated with diffuse thickening of the dura and arachnoid mater. The earliest described cases were associated with tuberculosis and syphilis, but we now recognize a spectrum of potential causes.
IgG4 disease is a relatively new entity that should be considered in the context of any cryptic/idiopathic infiltrative process!
Even with a rare disease (unknown to many in the room), we were able to build a DDx for pachymeningitis using the “Big Three” categories of medicine: Infection, Rheumatologic/Inflammatory, and Malignancy. We were also able to take a page out of our playbook for infiltrative diseases.
The DDx for pachymeningitis includes:
1) Infection: Tuberculosis, Syphilis
2) Rheum/Inflammatory: IgG4 disease, neurosarcoidosis, granulomatosis w/ polyangiitis (GPA), rheumatoid arthritis, and idiopathic pachymeningitis (the last is a dx of exclusion)
3) Malignancy: Lymphoma, en plaque meningioma
For a brief anatomy review:
Meninges: the three membranes that cover the brain and spinal cord
1) pia mater (closest to the CNS structures)
2) arachnoid mater
3) dura mater (furthest from CNS structures)
Leptomeninges = pia/arachnoid mater
Pachymeninges = arachnoid/dura mater