Inflammatory and Autoimmune Markers

Systemic inflammatory and autoimmune diseases frequently have neurologic manifestations, and recognizing these connections allows correct diagnosis and integrated multidisciplinary care. The inflammatory / autoimmune lab panel — ANA, anti-dsDNA, anti-Smith, anti-SSA/SSB (Ro/La), ANCA, complement levels (C3, C4, CH50), rheumatoid factor, anti-CCP, anti-thyroid antibodies, IgG4, ACE — is useful in evaluating patients with suspected vasculitis, connective tissue disease, sarcoidosis, IgG4-related disease, or autoimmune encephalopathy of unclear etiology. This page covers the major systemic autoimmune markers, their disease associations, neurologic manifestations, and the appropriate role of each in the neurologic workup.

Antinuclear Antibodies (ANA)

What ANA Detects

• Polyclonal antibodies against nuclear antigens.
• Screening test for connective tissue disease.
• Reported as titer + pattern (homogeneous, speckled, centromere, nucleolar, etc.).

Interpretation

• Low-titer positive (1:40-1:80): common in healthy individuals (especially elderly women); often non-specific.
• Medium-high titer (≥1:160): more likely clinically significant.
• Always interpret in clinical context: positive ANA in absence of clinical features rarely indicates disease.
• Patterns provide clues:
  • Homogeneous: SLE, drug-induced lupus.
  • Speckled: SLE, MCTD, Sjögren, scleroderma.
  • Centromere: CREST/limited scleroderma.
  • Nucleolar: scleroderma.
  • Cytoplasmic: Jo-1 (myositis), AMA (PBC).

Disease-Specific Antibodies After Positive ANA

• Anti-dsDNA: highly specific for SLE; titer correlates with disease activity, especially lupus nephritis.
• Anti-Smith (anti-Sm): highly specific for SLE; not titer-correlated.
• Anti-SSA (Ro) / SSB (La): Sjögren syndrome, SLE; neonatal lupus and congenital heart block in fetus of antibody-positive mother.
• Anti-RNP: mixed connective tissue disease.
• Anti-Scl-70: diffuse scleroderma.
• Anti-centromere: limited scleroderma/CREST.
• Anti-Jo-1, anti-Mi-2, anti-MDA5, anti-TIF1γ, anti-NXP2: dermatomyositis/polymyositis subtypes.

Neurologic Manifestations of SLE

“Neuropsychiatric SLE” — Wide Spectrum

• Cognitive impairment (common, often subtle).
• Headache.
• Psychiatric: depression, anxiety, psychosis.
• Seizures.
• Stroke (often related to antiphospholipid antibodies).
• Myelitis.
• Peripheral neuropathy.
• Cerebral venous sinus thrombosis.
• Cognitive dysfunction, “lupus fog.”

Diagnostic Approach

• ANA + anti-dsDNA / Smith + complement (C3, C4 — often low in active SLE).
• Antiphospholipid antibodies (frequent in SLE).
• CSF often nonspecifically abnormal in CNS lupus.
• MRI may show small vessel ischemic changes, white matter lesions.

Sjögren Syndrome

Neurologic Manifestations

• Peripheral neuropathies:
  • Sensory ganglionopathy (sensory ataxia, no motor involvement).
  • Small fiber neuropathy (painful, with autonomic features).
  • Length-dependent polyneuropathy.
• Cranial neuropathies (especially trigeminal).
• CNS involvement: optic neuritis, transverse myelitis, NMOSD-like (some Sjögren patients have AQP4-IgG).
• Cognitive dysfunction.

Diagnostic Approach

• Anti-SSA (Ro52, Ro60) and anti-SSB (La).
• Schirmer test, salivary gland biopsy (focus score) — see Tissue Diagnostics page.
• Sicca symptoms (dry eyes, dry mouth).

ANCA-Associated Vasculitides

The Three Syndromes

• Granulomatosis with polyangiitis (GPA, formerly Wegener): PR3-ANCA / c-ANCA.
• Microscopic polyangiitis (MPA): MPO-ANCA / p-ANCA.
• Eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss): MPO-ANCA / p-ANCA in ~40%.

Neurologic Manifestations

• Mononeuritis multiplex: classic for vasculitis (asymmetric, painful, multiple individual nerves involved).
• Distal symmetric polyneuropathy.
• Cranial neuropathies.
• Stroke (CNS vasculitis).
• Hypertrophic pachymeningitis (especially GPA).
• Hearing loss, ENT involvement (especially GPA).
• Asthma + eosinophilia + neuropathy → think EGPA.

Testing

• p-ANCA (MPO target) and c-ANCA (PR3 target).
• Indirect immunofluorescence + ELISA/multiplex for specific target.
• Eosinophil count (EGPA).
• Urinalysis (glomerulonephritis common).
• CSF in CNS vasculitis (often abnormal).
• Nerve and tissue biopsy can confirm vasculitis.

Complement (C3, C4, CH50)

Low Complement

• Active SLE: low C3, C4 reflects immune complex consumption.
• Hereditary complement deficiencies: risk for SLE-like disease, recurrent infection.
• CH50 measures total classical pathway activity.

High Complement

• Acute phase response (not usually clinically informative).

Rheumatoid Factor and Anti-CCP

Rheumatoid Arthritis Neurologic Manifestations

• Atlantoaxial subluxation (cervical instability from rheumatoid pannus); myelopathy.
• Mononeuritis multiplex (rheumatoid vasculitis).
• Carpal tunnel and other entrapment neuropathies.
• Cervical myelopathy.
• Drug-related: methotrexate-associated leukoencephalopathy, TNF-inhibitor demyelination.

Testing

• Rheumatoid factor: IgM against IgG Fc; positive in ~70% RA but also in chronic infection, other autoimmune disease, normal elderly.
• Anti-CCP (cyclic citrullinated peptide): more specific for RA (~95%); positive earlier in disease.

Sarcoidosis — Imaging + Tissue, Not ACE

Neurologic Manifestations (Neurosarcoidosis)

• Cranial neuropathies (especially facial — bilateral facial palsy is highly suggestive).
• Hypothalamic-pituitary dysfunction.
• Hydrocephalus.
• Basilar meningitis.
• Myelopathy.
• Peripheral neuropathy / small fiber neuropathy.
• Encephalopathy.

Workup — Priority Order

Modern neurosarcoidosis workup is imaging- and tissue-driven, not serum-biomarker-driven. Serum ACE has limited standalone value, especially in isolated neurosarcoidosis.

1. Imaging: brain MRI (leptomeningeal enhancement, parenchymal lesions, hypothalamic-pituitary involvement); chest CT for pulmonary sarcoidosis (the most likely systemic site); whole-body FDG-PET to identify biopsy targets when initial workup is unrevealing.
2. Systemic-organ search: skin, eye (slit-lamp), lymph nodes, hypercalcemia/calcitriol, ECG/echo for cardiac involvement.
3. Tissue biopsy: lymph node, lung, conjunctiva, salivary gland — non-caseating granulomas. Tissue is the gold standard when accessible.
4. Clinicoradiographic pattern recognition: bilateral facial palsy, hypothalamic dysfunction, basilar meningitis, hypertrophic pachymeningitis.
5. Serum/CSF ACE: supportive but low-yield as a stand-alone test — serum ACE is only ~60% sensitive and not specific; CSF ACE is even less sensitive. Do not anchor diagnosis on ACE alone.

Anti-Thyroid Antibodies — Hashimoto Encephalopathy / SREAT

Concept

• SREAT (Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis): anti-thyroid antibody-positive encephalopathy, often steroid-responsive.
• Anti-thyroid peroxidase (anti-TPO) and/or anti-thyroglobulin antibodies.
• May be euthyroid — antibody positivity reflects autoimmune predisposition, not necessarily thyroid dysfunction.

Clinical Features

• Subacute confusion, cognitive decline.
• Myoclonus, tremor, seizures, stroke-like episodes.
• Psychiatric features.
• CSF often shows elevated protein.
• EEG: diffuse slowing.

Diagnosis (of Exclusion)

• Anti-TPO and/or anti-Tg positive.
• Exclude infectious, structural, paraneoplastic, autoimmune encephalitis with cell-surface antibodies.
• Steroid responsiveness is part of the diagnostic concept.

Treatment

• High-dose steroids.
• IVIG or plasmapheresis if steroid-refractory.

IgG4-Related Disease

Neurologic Manifestations

• Hypertrophic pachymeningitis.
• Hypophysitis.
• Orbital pseudotumor.
• Trigeminal nerve enlargement.
• Often coexisting with other organ involvement (pancreatitis, sialadenitis, lymphadenopathy).

Testing

• Serum IgG4 elevated (in most but not all).
• Tissue biopsy with IgG4+ plasma cells, storiform fibrosis, obliterative phlebitis.

Cryoglobulinemia

Neurologic Manifestations

• Peripheral neuropathy (often painful, distal, mononeuritis multiplex pattern).
• CNS vasculitis (rare).

Testing

• Cryoglobulins (require special collection — warm tube).
• Often associated with hepatitis C, hematologic malignancy, autoimmune disease.

Behçet Disease

Neurologic Manifestations

• Brainstem syndromes (especially basal ganglia, midbrain).
• Cerebral venous sinus thrombosis.
• Aseptic meningitis.
• Cognitive decline.

Testing

• No specific serology; clinical diagnosis with oral/genital ulcers, ocular involvement.
• HLA-B51 association.
• Pathergy test.

Practical Approach

When to Order Inflammatory / Autoimmune Markers

• Suspected vasculitis (mononeuritis multiplex, multifocal neurologic syndrome, abnormal urinalysis, systemic features).
• Suspected connective tissue disease (autoimmune encephalopathy, peripheral neuropathy with sicca symptoms, young stroke).
• Subacute encephalopathy of unclear etiology after autoimmune encephalitis panel.
• Suspected sarcoidosis (cranial neuropathies, especially bilateral facial palsy, basilar meningitis, hypothalamic dysfunction).
• Cervical myelopathy in known RA.
• Mononeuritis multiplex with eosinophilia and asthma (EGPA).

Common Pitfalls

• Low-titer ANA: common, often non-specific; don’t over-interpret.
• Elevated ACE: many false positives; not pathognomonic for sarcoidosis.
• Anti-thyroid antibodies: very common in healthy population; SREAT diagnosis requires clinical syndrome + exclusion of alternatives.
• Rheumatoid factor: low specificity; anti-CCP more useful.
• Inflammatory markers without clinical features: usually not informative.

Pitfalls and Pearls

• ANA: screening; low-titer common and non-specific; high-titer + clinical features more meaningful.
• SLE-specific: anti-dsDNA (titer reflects activity), anti-Smith (specific not titer-correlated).
• SLE + low C3/C4: active disease.
• Neuropsychiatric SLE: many syndromes; APS antibodies often coexisting.
• Sjögren neuropathies: sensory ganglionopathy, SFN, length-dependent.
• Sjögren + AQP4: NMOSD can coexist.
• ANCA + mononeuritis multiplex: think vasculitis (GPA, MPA, EGPA).
• Asthma + eosinophilia + neuropathy: EGPA.
• Bilateral facial palsy: short differential — Lyme, sarcoidosis, GBS, HIV.
• Neurosarcoidosis: cranial neuropathies, basilar meningitis, hypothalamic dysfunction.
• Serum ACE: only ~60% sensitive; not specific.
• Rheumatoid arthritis cervical instability: atlantoaxial subluxation, myelopathy.
• Hashimoto encephalopathy (SREAT): anti-TPO positive; diagnosis of exclusion; steroid responsive.
• IgG4-related disease: hypertrophic pachymeningitis, hypophysitis, orbital pseudotumor.
• Cryoglobulinemia: painful peripheral neuropathy; HCV common.
• Behçet: brainstem syndromes, CVT; oral/genital ulcers; HLA-B51.
• Order inflammatory panel when clinical features suggest: not as routine screening.

References

1. Hanly JG, Urowitz MB, Su L, et al. Prospective analysis of neuropsychiatric events in an international disease inception cohort of patients with systemic lupus erythematosus. Ann Rheum Dis. 2010;69(3):529-535.
2. 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.
3. Berkowitz AL, Samuels MA. The neurology of Sjögren syndrome and the rheumatology of peripheral neuropathy and myelitis. Pract Neurol. 2014;14(1):14-22.
4. Castañeda S, Blanco R, González-Gay MA. Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Curr Opin Rheumatol. 2014;26(3):237-244.
5. Castillo P, Woodruff B, Caselli R, et al. Steroid-responsive encephalopathy associated with autoimmune thyroiditis. Arch Neurol. 2006;63(2):197-202.
6. AbdelRazek MA, Venna N, Stone JH. IgG4-related disease of the central and peripheral nervous systems. Lancet Neurol. 2018;17(2):183-192.