Neurosarcoidosis
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Direct answer
Granulomas that seed the nervous system produce neurosarcoidosis, whose commonest presentation is cranial neuropathy — facial palsy, often bilateral or recurrent — followed by basal leptomeningitis with headache and hydrocephalus, hypothalamic-pituitary infiltration with diabetes insipidus or amenorrhoea-galactorrhoea, parenchymal mass lesions, myelopathy, and a peripheral neuropathy that can mimic Guillain-Barré syndrome. Because isolated neurological sarcoidosis is uncommon, the diagnosis leans on proving systemic disease: chest imaging for bilateral hilar lymphadenopathy, cutaneous lesions such as erythema nodosum or lupus pernio, uveitis on slit-lamp examination, raised serum and CSF angiotensin-converting enzyme, and FDG-PET to find a biopsyable target. Histology — non-caseating granulomas — remains the gold standard. Treatment is prolonged high-dose corticosteroids with steroid-sparing agents (methotrexate, azathioprine, mycophenolate) and infliximab for refractory disease, and the great Indian caveat is tuberculosis, which imitates every single feature.
What you must remember
- Cranial nerve hierarchy: facial nerve (frequently bilateral, sometimes recurrent) first; optic nerve second with papilloedema or optic neuropathy; vestibulocochlear, trigeminal and multiple neuropathies follow.
- Basal meningeal picture: gadolinium enhancement of the basal leptomeninges and optic chiasm on MRI, with headache, hydrocephalus (sometimes the presenting emergency) and cranial neuropathies in series.
- Neuroendocrine face: hypothalamic and pituitary stalk involvement — diabetes insipidus, hyperprolactinaemia, sleep-wake and appetite disturbance; a thickened enhancing stalk on MRI is a signature.
- Systemic screen battery: high-resolution chest CT (hilar nodes, interstitial pattern), ophthalmology for uveitis, skin examination, serum calcium and ACE, and CSF (lymphocytic pleocytosis, raised protein, ACE variably positive — oligoclonal bands may be present and do not exclude it).
- Diagnostic standards: possible neurosarcoidosis requires a compatible syndrome with laboratory or histological systemic sarcoidosis; definite requires nervous-system histology (Zajicek framework) — biopsy reserved for accessible lesions or dangerous mimics.
- Treatment ladder: prednisolone 0.5-1 mg/kg for months with slow taper (relapse-prone disease); methotrexate or azathioprine as steroid-sparing; infliximab for refractory; hydrocephalus and mass lesions may need neurosurgery.
- The tuberculosis shadow: in India, basal meningitis with cranial palsies is tuberculous until excluded — contrast the CSF (low glucose with high protein and lymphocyte predominance favours TB), chest imaging, and where doubt persists, biopsy or a documented therapeutic decision made jointly.
Working through a bilateral facial palsy
A 34-year-old teacher develops left facial weakness, and three weeks later the right side follows — a bilateral lower motor neuron facial palsy, which is never Bell's palsy by definition. The screen for bilateral VII palsy is short and examinable: sarcoidosis, Lyme disease (travel history), Guillain-Barré variant (areflexia, albuminocytological dissociation), HIV and lymphoma/leukaemia. Her chest radiograph shows bilateral hilar fullness; slit-lamp examination reveals anterior uveitis; serum ACE is raised; CSF shows lymphocytic pleocytosis with protein elevation. She has Löfgren-spectrum systemic sarcoidosis with neurological involvement, and prednisolone 60 mg daily with a taper over six months, plus methotrexate after the second relapse, restores facial function. Had her MRI instead shown nodular enhancement along the basal cisterns with hydrocephalus and her CSF a low glucose, the working diagnosis in an Indian ward tilts decisively to tuberculous meningitis, and the management conversation is about anti-tubercular therapy duration and steroids — not an academic distinction, since infliximab in unrecognised disseminated tuberculosis could be catastrophic.
Where candidates slip
The error pattern is twofold: accepting "sarcoid-like" radiology without a systemic hunt (every presumed neurosarcoidosis case needs chest CT, eye examination and a biopsy of something reachable), and forgetting that CSF oligoclonal bands appear in sarcoidosis, wrongly hard-coding them to multiple sclerosis. The exam's favourite discriminating pair is neurosarcoidosis versus tuberculous meningitis — lymphocytic pleocytosis with normal glucose and enhancing stalk favour the former; low CSF glucose with basal exudates and chest consolidation favour the latter. For Indian candidates this is not exam trivia but ward reality, and a viva answer that mentions tissue confirmation before committing to months of immunosuppression earns its marks.
Frequently asked questions
Which cranial nerve is most commonly involved in neurosarcoidosis?
The facial nerve, frequently bilaterally or recurrently — bilateral lower motor neuron facial palsy should always trigger a sarcoid screen.
What MRI pattern is characteristic of neurosarcoidosis?
Basal leptomeningeal and dural gadolinium enhancement, often with optic pathway involvement, hypothalamic-pituitary stalk thickening, hydrocephalus or enhancing parenchymal lesions.
Which systemic findings support neurosarcoidosis?
Bilateral hilar lymphadenopathy, uveitis, erythema nodosum or lupus pernio, hypercalcaemia and raised angiotensin-converting enzyme, with non-caseating granulomas on histology.
Which first-line drug and which steroid-sparing strategy treat neurosarcoidosis?
Prolonged oral prednisolone with slow taper, plus methotrexate or azathioprine for relapsing or steroid-dependent disease; infliximab for refractory cases.
Why must tuberculosis be excluded before immunosuppressing a suspected neurosarcoidosis case?
Tuberculous basal meningitis mimics the clinical and imaging picture, and steroids, methotrexate or infliximab can unmask disseminated tuberculosis.