What is pachymeningitis?

What is Pachymeningitis?

Pachymeningitis is a fibrosing and inflammatory process that involves the dura mater (the outermost meningeal layer), characterized by thickening and contrast enhancement of this membrane on MRI imaging. 1

Anatomic Distribution and Clinical Manifestations

Pachymeningitis can affect different anatomic locations with distinct clinical presentations:

• Cranial pachymeningitis presents with headaches and cranial nerve palsies due to compression of adjacent cranial nerves 1
• Spinal pachymeningitis causes nerve root or spinal cord compression symptoms 1
• Combined cranial and spinal involvement occurs less frequently but can present with both symptom patterns simultaneously 1

The inflammatory lesions compress adjacent nervous structures, producing symptoms based on their specific location 2. In Rosai-Dorfman-Destombes disease, intracranial RDD can cause diffuse pachymeningitis, though the most common radiographic appearance is a solitary extraaxial, homogeneously enhancing dural mass mimicking a meningioma 3.

Pathophysiology

The underlying pathogenic mechanism involves:

• Inflammatory infiltrate consisting mainly of B and T lymphocytes that activates fibroblasts 2
• Collagen deposition leading to tissue hypertrophy and increased dural thickness 2
• Three central pathological features: lymphoplasmacytic infiltration, obliterative phlebitis, and storiform fibrosis 2

Etiologic Classification

Pachymeningitis is divided into secondary (with identifiable cause) and idiopathic forms:

Secondary causes include:

• Infectious etiologies: syphilis, tuberculosis, and other infections 1
• Inflammatory/autoimmune diseases: sarcoidosis, granulomatosis with polyangiitis (GPA), IgG4-related disease 1, 4
• Neoplastic processes 2
• ANCA-associated vasculitis: GPA rarely involves meningeal inflammation, but around two-thirds of HP cases related to GPA have positive serum ANCA 4

Idiopathic hypertrophic pachymeningitis (IHP) is diagnosed when no known etiology can be identified after comprehensive evaluation 5, 1. Recently, IgG4-related disease has been recognized as representing a subset of cases previously diagnosed as IHP 2.

Diagnostic Approach

MRI is the examination of choice for preliminary diagnosis, showing contrast enhancement and thickening of the dura mater 1, 2. The characteristic MRI findings include dural thickening with contrast enhancement 4.

Histopathological examination of a dura mater biopsy specimen provides definitive diagnosis confirmation 2. However, diagnosis often requires exclusion of all other known etiologies, particularly in suspected IHP cases 5.

Laboratory evaluation should include:

• Inflammatory markers (often elevated) 4
• Autoimmune testing including rheumatoid factor and ANCA 4
• IgG4 levels when IgG4-related disease is suspected 2

Treatment Strategy

Corticosteroids are the main first-line treatment for pachymeningitis 1. The typical approach involves:

• Initial treatment with high-dose corticosteroids (intravenous methylprednisolone) 5
• Transition to oral prednisone for maintenance 5

Second-line immunosuppressive therapy is indicated for:

• Steroid-refractory cases 5, 2
• Recurrence following steroid taper 5
• Need for steroid-sparing agents 2

Rituximab is the preferred second-line agent for patients who do not respond to glucocorticoids or conventional steroid-sparing agents 5, 2. It has demonstrated efficacy in steroid-refractory pachymeningitis and as treatment for ANCA-associated disease 5.

Intraventricular chemotherapy with methotrexate, cytarabine, and dexamethasone should be considered for treatment-refractory HP with persistent intrathecal inflammation before irreversible cranial nerve damage occurs 6.

Important Clinical Pitfalls

• Steroid taper complications: Recurrent headaches commonly follow steroid taper, potentially due to corticosteroid withdrawal or ongoing inflammation 5
• Diagnostic mimicry: IHP often mimics other inflammatory conditions including neurosarcoidosis, GPA, and IgG4-related disease, requiring extensive workup to exclude secondary causes 5
• Delayed diagnosis: The rarity of this condition and symptom overlap with other neurologic disorders can lead to diagnostic delays 4
• Psychiatric complications: Treatment with intraventricular chemotherapy can exacerbate psychiatric symptoms 6