Neurosarcoidosis & CNS Vasculitis

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Neurosarcoidosis & CNS Vasculitis

Neurosarcoidosis and CNS vasculitis represent two categories of inflammatory neurologic disease that pose significant diagnostic challenges. Neurosarcoidosis is the neurologic manifestation of a systemic granulomatous disorder that can affect virtually any component of the nervous system. CNS vasculitis encompasses a group of disorders characterized by inflammation of cerebral, meningeal, or spinal vasculature, which may be primary (primary angiitis of the CNS) or secondary to systemic inflammatory, infectious, or neoplastic conditions. Both entities share the challenge of requiring tissue confirmation for definitive diagnosis and have overlapping differential diagnoses. This topic also covers hypertrophic pachymeningitis, a related inflammatory condition of the dura mater with multiple etiologies including sarcoidosis, IgG4-related disease, and vasculitis.

Bottom Line

Neurosarcoidosis: Neurologic involvement occurs in 5–10% of sarcoidosis patients; one-third have NO systemic disease at diagnosis; cranial neuropathies (especially bilateral facial palsy) are the most common CNS manifestation
Spinal cord sarcoidosis: The trident sign (dorsal subpial + central canal enhancement on axial MRI) is characteristic; longitudinally extensive T2 lesions are most frequent; imaging abnormalities are often out of proportion to clinical deficits
Diagnosis: 2018 Consensus Criteria classify neurosarcoidosis as Possible, Probable, or Definite based on clinical, investigational, and pathologic findings; serum ACE and soluble IL-2 receptor are NOT recommended due to poor specificity
Treatment: Corticosteroids remain the cornerstone; current trend is toward early infliximab + methotrexate combination to allow steroid taper; infliximab is the preferred steroid-sparing agent
CNS vasculitis: Can be primary (PACNS) or secondary; MRI shows multifocal infarcts and hemorrhages; conventional angiography shows vessel "beading"; biopsy often required for definitive PACNS diagnosis
Susac syndrome: Triad of encephalopathy + branch retinal artery occlusions + sensorineural hearing loss; snowball lesions in corpus callosum on MRI; limited forms are common
Hypertrophic pachymeningitis: Focal or diffuse dural thickening with a broad differential; IgG4-related disease is an important and treatable cause; biopsy often necessary when serologic workup is negative

Neurosarcoidosis

Epidemiology

Sarcoidosis incidence: 1–15 per 100,000/year depending on population and geography
Neurologic involvement in approximately 5–10% of patients with systemic sarcoidosis
Higher incidence in Black Americans
North-south gradient similar to multiple sclerosis
Neurosarcoidosis is typically diagnosed within 2 years of systemic sarcoidosis diagnosis
One-third of patients with neurosarcoidosis have NO systemic manifestations at the time of neurologic diagnosis — making isolated neurosarcoidosis a particularly challenging diagnosis

Pathology

Sarcoidosis is a multisystem granulomatous disorder characterized by non-necrotizing (non-caseating) granulomatous inflammation. The granulomas consist of tightly clustered epithelioid histiocytes and multinucleated giant cells, with a rim of CD4+ T lymphocytes. The most commonly affected systemic sites include lungs, skin, joints, and eyes. When the nervous system is involved, granulomatous inflammation can affect the meninges, cranial nerves, brain parenchyma, spinal cord, and peripheral nerves.

Clinical Manifestations

Manifestation	Key Features	Imaging/Investigations
Meningitis	Most commonly leptomeningeal with basilar predominance; headache, cranial neuropathies; communicating hydrocephalus may develop	MRI: basilar leptomeningeal enhancement; CSF: pleocytosis, elevated protein, low glucose, oligoclonal bands
Cranial neuropathies	Most common CNS manifestation overall; facial nerve most frequently affected (often bilateral); optic nerve and vestibulocochlear nerve also common; can occur with or without meningitis	MRI: cranial nerve enhancement; may see associated meningeal thickening
Brain parenchymal disease	Hypothalamus, pituitary, and infundibulum most commonly affected; discrete enhancing lesions or diffuse involvement; headache, focal neurologic signs, seizures; often associated with concurrent meningeal disease	MRI: enhancing parenchymal lesions, hypothalamic/pituitary masses; may mimic neoplasm
Spinal cord disease	Subacute or chronic myelopathy; any spinal cord level; longitudinally extensive T2 lesions most frequent; imaging abnormalities often out of proportion to clinical features (unlike NMOSD where clinical deficits are more severe)	MRI: longitudinally extensive T2 lesions; trident sign on axial imaging (linear dorsal subpial enhancement + central canal enhancement); ventral subpial “braid” pattern
Peripheral nerve	Small fiber neuropathy (both sensory and autonomic) most common PNS manifestation; combined CNS and PNS involvement is rare	Skin biopsy for intraepidermal nerve fiber density; nerve conduction studies; autonomic function testing

The Trident Sign in Spinal Cord Sarcoidosis

On axial MRI of the spinal cord, the trident sign comprises three distinct points of enhancement: two dorsal subpial foci and one central canal focus
The dorsal subpial enhancement appears as linear enhancement along the dorsal surface of the cord
A ventral subpial “braid” pattern of enhancement has also been described and is suggestive of sarcoidosis
These patterns reflect the predilection of granulomatous inflammation for the subpial and perivascular spaces
Key distinction from NMOSD: In spinal cord sarcoidosis, imaging abnormalities are often extensive but clinical manifestations are relatively mild; in NMOSD, clinical severity typically matches or exceeds the imaging findings

Diagnostic Criteria

The 2018 Neurosarcoidosis Consortium Consensus Group established diagnostic criteria based on a combination of clinical presentation, supportive investigations, and pathologic confirmation:

Diagnostic Level	Requirements
Possible	Typical clinical presentation consistent with granulomatous inflammation of the nervous system + supportive investigations (MRI, CSF, PET-CT) + exclusion of alternative diagnoses + no pathologic confirmation
Probable	Typical clinical presentation + supportive investigations + pathologic confirmation of systemic granulomatous disease outside the nervous system (e.g., lung, lymph node, skin biopsy showing non-caseating granulomas)
Definite — Type A	Pathologic confirmation of granulomatous disease of the nervous system lesion + evidence of systemic sarcoidosis
Definite — Type B	Pathologic confirmation of granulomatous disease of the nervous system lesion + isolated neurosarcoidosis (no systemic disease identified)

Investigations

Category	Tests	Notes
Serologic	CBC, renal and liver function, vitamin D, calcium, quantitative immunoglobulins	Hypercalcemia and elevated 1,25-dihydroxyvitamin D support sarcoidosis diagnosis
To exclude mimics	ANCA, IgG4, GFAP IgG, MOG IgG, AQP4 IgG, HIV, Lyme, TB (IGRA), syphilis	Extensive workup essential given broad differential of granulomatous inflammation
CSF	Cell count, protein, glucose, oligoclonal bands, viral studies, bacterial/fungal cultures, TB studies, syphilis serology, cytology, flow cytometry	Cytology and flow cytometry important to exclude lymphoma, which can mimic neurosarcoidosis
Imaging	Brain and spine MRI with contrast; chest CT; PET-CT	PET-CT is more sensitive than chest CT for detecting systemic sarcoidosis and identifying biopsy targets
Additional	Bone marrow biopsy, tissue biopsy of accessible lesions, ECG, ophthalmologic examination (including slit-lamp), pulmonary function testing	Tissue biopsy of the most accessible site (lymph node, skin, lung) is preferred over nervous system biopsy when possible

Serum ACE and Soluble IL-2 Receptor Are NOT Recommended

Serum angiotensin-converting enzyme (ACE) is frequently ordered but has poor sensitivity and specificity for neurosarcoidosis
Soluble IL-2 receptor (sIL-2R) is similarly nonspecific
Both markers can be elevated in lymphoma and neurotuberculosis — two critical diagnoses that must be excluded before diagnosing neurosarcoidosis
Reliance on these biomarkers may lead to premature diagnostic closure and missed alternative diagnoses
The Neurosarcoidosis Consortium Consensus Group does not recommend using these markers as part of the diagnostic workup

Treatment of Neurosarcoidosis

Acute Management

Corticosteroids remain the cornerstone of acute neurosarcoidosis treatment:

Intravenous methylprednisolone (IVMP): 1 g/day for 3–5 days for acute, severe presentations
Oral prednisone: 60–80 mg/day following IV pulse, with gradual taper

Traditional Approach vs. Current Trend

Approach	Strategy	Limitations/Benefits
Traditional	Prolonged high-dose corticosteroids for 2–3 months with slow taper over 6–12 months	Limited by cumulative steroid side effects (weight gain, diabetes, osteoporosis, cataracts, avascular necrosis, infection risk)
Current trend	Infliximab + methotrexate combination introduced early, allowing more rapid corticosteroid taper	Methotrexate serves dual purpose: steroid-sparing agent AND prevents formation of antibodies to infliximab; combination allows faster reduction of steroid burden

Steroid-Sparing Agents

Agent	Dosing	Notes
Infliximab	3–5 mg/kg IV at weeks 0, 2, and 6, then every 4–8 weeks	Anti-TNF-α monoclonal antibody; considered the preferred steroid-sparing agent; best used with methotrexate to prevent anti-drug antibodies
Methotrexate	10–25 mg/week orally or subcutaneously	Often combined with infliximab; also used as monotherapy for mild disease; supplement with folic acid
Rituximab	1000 mg IV ×2 separated by 2 weeks, then every 6 months	Anti-CD20 monoclonal antibody; considered for infliximab-refractory disease
Azathioprine	2–3 mg/kg/day orally	Purine synthesis inhibitor; check TPMT activity before initiation
Mycophenolate mofetil	1000–1500 mg twice daily	Inhibits inosine monophosphate dehydrogenase; generally well tolerated
Cyclophosphamide	Variable (pulse IV or daily oral)	Reserved for severe, refractory cases; significant toxicity profile
Adalimumab	40 mg SC every 2 weeks	Alternative anti-TNF-α agent; less studied than infliximab in neurosarcoidosis

Treatment Duration and Monitoring

For moderate-to-severe first presentations, treat for a few years then consider cessation with careful monitoring for relapse
Relapse may necessitate longer — potentially indefinite — treatment duration
Monitor with serial MRI (brain and/or spine as appropriate), clinical examination, and CSF analysis in select cases
PET-CT may be useful for monitoring systemic disease activity and guiding treatment decisions
Corticosteroid taper should be individualized; aim to minimize cumulative steroid exposure while maintaining disease control

CNS Vasculitis

Overview

CNS vasculitis encompasses a group of disorders caused by inflammation of cerebral, meningeal, or spinal vasculature. It can be classified as:

Primary angiitis of the CNS (PACNS): Inflammation isolated to the CNS vasculature with no systemic vasculitis
Secondary CNS vasculitis: CNS vascular inflammation occurring in the context of systemic inflammatory, infectious, or neoplastic disease

CNS vasculitis is further classified by the size of vessels predominantly affected (large, medium, or small), which influences the clinical presentation, imaging findings, and diagnostic approach.

Clinical Presentation

Subacute headaches — often the earliest and most common symptom
Cognitive changes — insidious decline in memory, attention, and executive function
Focal neurologic symptoms — reflecting the territory of affected vessels (hemiparesis, aphasia, visual deficits)
Seizures — may be the presenting manifestation
Stroke or TIA — particularly in medium-to-large vessel involvement
Symptoms are typically subacute and progressive, distinguishing CNS vasculitis from acute thromboembolic stroke

Investigations for CNS Vasculitis

Investigation	Findings	Limitations
Brain MRI	Multifocal infarcts in different vascular territories and of different ages; SWI sequences show hemorrhages; meningeal enhancement may be present	Findings are nonspecific and overlap with many other conditions
CSF analysis	Elevated WBC (lymphocytic pleocytosis) and protein; may be normal in up to 10–20% of cases	Nonspecific; important for excluding infection and malignancy
Conventional cerebral angiography	Alternating areas of vessel narrowing and dilation (“beading”); vessel occlusion; delayed circulation time	Sensitivity ~50–70% for biopsy-proven PACNS; cannot differentiate vasculitis from vasospasm, atherosclerosis, or RCVS
Vessel wall MRI	Concentric vessel wall enhancement and thickening in inflammatory vasculitis	Differentiates inflammatory (concentric enhancement) from atherosclerotic (eccentric enhancement) disease; emerging modality
Brain and meningeal biopsy	Transmural inflammatory infiltrate with vessel wall destruction; granulomatous, lymphocytic, or necrotizing patterns	Invasive; sampling error is significant (sensitivity ~50–75%); often necessary for definitive PACNS diagnosis

Reversible Cerebral Vasoconstriction Syndrome (RCVS) — Critical Differential

RCVS is the most important mimic of CNS vasculitis and must be excluded before initiating immunosuppressive therapy
Thunderclap headaches (sudden severe headache reaching maximum intensity in <1 minute) are the hallmark — CNS vasculitis headaches are subacute and progressive
Angiography shows reversible multifocal vasoconstriction that resolves within 3 months (similar “beading” pattern to vasculitis)
Associated with serotonergic medications (triptans, SSRIs, SNRIs), sympathomimetics, cannabis, and the postpartum period
CSF is typically normal in RCVS (unlike CNS vasculitis where CSF is usually abnormal)
Treatment of RCVS: removal of offending agent, supportive care, calcium channel blockers; corticosteroids may worsen RCVS

Secondary Causes of CNS Vasculitis

The differential diagnosis for secondary CNS vasculitis is broad and includes all conditions that can also cause pachymeningitis, plus additional systemic vasculitides:

Category	Conditions
Connective tissue diseases	Rheumatoid arthritis, Sjögren syndrome, systemic lupus erythematosus, Behçet disease
IgG4-related disease	Can cause both pachymeningitis and vasculitis; elevated serum IgG4 and tissue IgG4+ plasma cells
Sarcoidosis	Granulomatous vasculitis; may occur with other neurosarcoidosis manifestations
ANCA-associated vasculitis	Granulomatosis with polyangiitis (GPA), microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis (EGPA)
Large vessel vasculitis	Giant cell arteritis (temporal arteritis), Takayasu arteritis
Amyloid-related	Cerebral amyloid angiopathy with related inflammation (CAA-ri) / amyloid beta-related angiitis (ABRA); particularly in older patients; emerging concern with anti-amyloid monoclonal antibody therapies

Susac Syndrome

Susac Syndrome: Key Features

Classic triad: Encephalopathy + branch retinal artery occlusions + sensorineural hearing loss
Pathophysiology: Autoimmune endotheliopathy affecting arterioles of the brain, retina, and cochlea
MRI: “Snowball” lesions in the central fibers of the corpus callosum (highly characteristic); may also affect periventricular white matter, deep gray matter, cerebellum, and brainstem
Fundoscopy: Gass plaques (hyperfluorescent arteriolar wall deposits on fluorescein angiography) are pathognomonic
Limited forms are common: Many patients present with only one or two components of the triad, making diagnosis challenging; the full triad may evolve over weeks to months
Treatment: Immunosuppression (corticosteroids, IVIg, mycophenolate, azathioprine); anticoagulation is debated; most patients have a self-limited monophasic course but residual deficits are common

Hypertrophic Pachymeningitis

Overview

Hypertrophic pachymeningitis refers to focal or diffuse thickening and inflammation of the dura mater. It can cause headaches, cranial neuropathies (particularly involving nerves passing through the skull base), seizures, and progressive neurologic deficits depending on the location and extent of dural involvement. MRI demonstrates enhancing dural thickening, which may be focal or diffuse.

Etiologies

Category	Specific Causes
Decreased intracranial pressure	CSF leak (spontaneous intracranial hypotension, post-procedural)
Infectious	Tuberculosis, syphilis, fungal infections
Neoplastic	Meningioma, lymphoma, metastatic disease, dural carcinomatosis
Inflammatory — Connective tissue	Rheumatoid arthritis, Sjögren syndrome, systemic lupus erythematosus, Behçet disease
Inflammatory — IgG4-related disease	An important and increasingly recognized cause; serum IgG4, tissue biopsy showing storiform fibrosis and IgG4+ plasma cells
Inflammatory — Granulomatous	Sarcoidosis, granulomatosis with polyangiitis (GPA)
Inflammatory — Other	Relapsing polychondritis, cryoglobulinemia, Cogan syndrome, polyarteritis nodosa
Inherited	Mucopolysaccharidoses
Idiopathic	Idiopathic hypertrophic pachymeningitis — diagnosis of exclusion when no systemic cause is identified

Diagnostic Approach

Evaluating Hypertrophic Pachymeningitis

MRI: Gadolinium-enhanced MRI demonstrates dural thickening and enhancement; assess distribution (focal vs. diffuse, convexity vs. skull base)
Serologic workup: ANCA (for GPA), IgG4 levels, IgG subclasses, ANA, dsDNA, RF, complement, ESR/CRP, ACE
CSF analysis: Cell count, protein, glucose, cytology, flow cytometry, cultures, IgG4 index
Systemic evaluation: CT chest (sarcoidosis, GPA), PET-CT (systemic inflammation), orbital/sinus imaging (GPA)
IgG4-related disease is an important cause that is increasingly recognized; serum IgG4 may be elevated but can be normal; tissue biopsy showing storiform fibrosis and ≥10 IgG4+ plasma cells per high-power field with IgG4:IgG ratio >40% is diagnostic
Biopsy is often necessary when serologic markers are negative and the etiology remains unclear; meningeal biopsy should target the area of maximal enhancement
If no systemic cause is identified after comprehensive evaluation, the diagnosis is idiopathic hypertrophic pachymeningitis

Diagnostic Comparison

Feature	Neurosarcoidosis	PACNS	Susac Syndrome	Hypertrophic Pachymeningitis
Typical age	20–50 years	40–60 years	20–50 years (F > M)	Any age
Headache	Common (meningitis)	Most common symptom	Common (encephalopathy)	Common
Cranial neuropathies	Very common (facial, optic)	Uncommon	VIII (hearing loss)	Common (skull base)
MRI pattern	Leptomeningeal enhancement, parenchymal lesions, cord lesions	Multifocal infarcts, hemorrhages	Snowball lesions in corpus callosum	Dural thickening/enhancement
CSF	Pleocytosis, ↑protein, ↓glucose, OCBs	↑WBC, ↑protein	Often normal or mild pleocytosis	Variable
Key diagnostic test	Tissue biopsy (extraneural or neural); PET-CT	Angiography + brain/meningeal biopsy	Fundoscopy (Gass plaques), audiometry, MRI	Biopsy; IgG4 serology
Systemic involvement	Lungs, skin, joints, eyes (67% at diagnosis)	None (by definition)	Retina, cochlea	Depends on cause

Treatment Overview

Condition	First-Line Treatment	Maintenance/Steroid-Sparing
Neurosarcoidosis	IVMP 1 g/day × 3–5 days → prednisone 60–80 mg/day with taper	Infliximab + methotrexate (preferred); alternatives: azathioprine, mycophenolate, rituximab
PACNS	High-dose corticosteroids (IVMP then oral prednisone)	Cyclophosphamide (induction); azathioprine or mycophenolate (maintenance)
Susac syndrome	Corticosteroids + IVIg	Mycophenolate, azathioprine; anticoagulation debated
IgG4-related pachymeningitis	Corticosteroids (usually highly responsive)	Rituximab (most effective steroid-sparing agent for IgG4-RD); mycophenolate, azathioprine
GPA-related pachymeningitis	Corticosteroids + cyclophosphamide or rituximab	Rituximab; azathioprine; mycophenolate
Idiopathic pachymeningitis	Corticosteroids	Steroid-sparing agents as needed; close monitoring for evolution to a defined etiology

References

McCombe JA. Neurologic manifestations of rheumatologic disorders. Continuum (Minneap Minn). 2024;30(4):1189-1225.
Zajicek JP, Scolding NJ, Foster O, et al. Central nervous system sarcoidosis—diagnosis and management. QJM. 1999;92(2):103-117.
Stern BJ, Royal W 3rd, Gelfand JM, et al. Definition and consensus diagnostic criteria for neurosarcoidosis: from the Neurosarcoidosis Consortium Consensus Group. JAMA Neurol. 2018;75(12):1546-1553.
Zalewski NL, Krecke KN, Weinshenker BG, et al. Central canal enhancement and the trident sign in spinal cord sarcoidosis. Neurology. 2016;87(7):743-744.