Although the etiology is unknown, sarcoidosis is a systemic disease that results in the formation of granulomas. Classically, the granulomas in sarcoidosis are non-caseating granulomas, which may be found throughout lymph nodes and organs, including the brain and nervous system. About 5% to 10% of patients with sarcoidosis will have neurologic complications. Although the majority of patients with sarcoidosis do not have symptoms, neurosarcoidosis may be life-threatening and tends to occur in cases with systemic involvement.
Although the cause is unclear, sarcoidosis is believed to be a hyperactive immune response. Th1 cells stimulate the release of IL-2 and IFN-gamma which then activate macrophages. In turn, the inflammatory response induced by macrophages causes granuloma formation.
The prevalence of sarcoidosis has been estimated to be about 152 to 215 per 100000. About 5% to 10% of patients with sarcoidosis will have neurologic complications. Regarding race, neurosarcoidosis has been documented more commonly within Africans and African descent. However, about half of patients with sarcoidosis have systemic disease, with 30% to 70% who have concomitant neurologic signs when first diagnosed.
A variety of theories have been used to explain the etiology of neurosarcoidosis. Sarcoidosis affects the lymphoreticular system, characterized by cervical and mediastinal lymphadenopathy. Due to the distribution of lymphatics, the spleen and liver can also be affected. Neurosarcoidosis results from sarcoid granulomas within the nervous system. Pathologically, lymphocytes, and mononuclear phagocytes surround a noncaseating epithelioid cell granuloma. Symptoms result from the location of where the granulomas lie in the nervous system. For example, granulomas in the muscle may cause myositis, while granulomas in the nerve within the perineurium and epineurium may cause axonal damage and as a result peripheral neuropathy. Nerve injury may cause diffuse polyneuropathy, mononeuritis multiplex, and polyradiculopathy due to spinal root sheath involvement.
The classical finding of sarcoidosis is noncaseating granulomas. Nerve biopsies demonstrate axonal degeneration with nerve atrophy. Myelin ovoids may be seen as a sign of demyelination.
Common features of central or peripheral nervous system involvement include: cranial mononeuropathy involving the facial nerve, neuroendocrine dysfunction involving the hypothalamus (i.e. neurogenic diabetes insipidus), myelopathy or radiculopathy if the spinal cord is affected (in rare cases cauda equina polyradiculopathy may occur), hydrocephalus, meningitis, mononeuropathy, mononeuritis multiplex, carpal tunnel, and muscle involvement which may cause proximal myopathy and muscle atrophy. Symptoms of neurosarcoidosis may be multifocal, commonly seen first in the cranial nerves. The facial nerve is the most common cranial nerve affected, which may mimic Lyme disease. Heerfordt syndrome is a rare manifestation of neurosarcoidosis which presents with facial nerve palsy and the presence of parotid gland enlargement, anterior uveitis, and fever. Carpal tunnel may also be more frequent in sarcoidosis patients than the rest of the population. Another cranial nerve that may be affected is the vestibulocochlear nerve causing balance and hearing problems. Cerebellar signs, such as ataxia, may be present with cerebellar involvement. During the exam, it is important to assess for papilledema and mental status as psychiatric abnormalities may also occur. Chronic meningitis with basal meningeal involvement is a common manifestation of neurosarcoidosis. Meningitis may present with either leptomeningeal or pachymeningeal involvement. It is one of the several important causes of pachymeningitis.
In gathering a history, the first sign of neurosarcoidosis may be seizures, which generally confers a poor prognosis. Patients with simple partial or complex partial seizures may have a better prognosis in comparison to generalized tonic-clonic seizures.
Neurosarcoidosis should be considered in patients with sarcoidosis who develop neurologic abnormalities. However, the index of suspicion is lower and thus much more difficult in cases where a patient is not known to have sarcoid but has neurologic abnormalities. Unfortunately, there is no diagnostic marker for neurosarcoidosis.
If neurosarcoidosis is suspected, it is important to assess for signs of systemic diseases, such as the skin, lymph nodes, and lungs. Tests to conduct include ophthalmologic exam (including optical coherence tomography), nasal/sinus examination, chest x-ray (for perihilar lymphadenopathy), angiotensin-converting enzyme (ACE) assay (not specific), and in rare cases a magnetic resonance, gallium or fluorodeoxyglucose emission tomographic scan for areas of inflammation that may be biopsied.
In evaluating peripheral neuropathy, it is important to rule out other common causes of neuropathy such as hyperglycemic states, vitamin deficiencies, kidney failure, and toxins. Thermal threshold testing may be used for small-fiber neuropathy.
Neurodiagnostic tests may help rule out other differentials such as infection and malignancy. The imaging of choice is a contrast-enhanced MRI. Typical findings are basal meningeal enhancement especially with contrast-enhancing lesions involving the hypothalamus, pituitary stalk, and adjacent tissues. (See MRI below). Gadolinium and fluid-attenuated inversion recovery (FLAIR) is helpful to identify T2 enhancement of nerve roots, plexuses, and nerves. Active inflammation may be seen with meningeal or parenchymal enhancement. Parenchymal, meningeal masses, and hydrocephalus may also be seen with MRI.
As with other inflammatory states, ESR may be elevated. Creatinine kinase and aldolase may also be used to evaluate for myopathy. Liver function testing may also be abnormal, thereby reflecting the systemic involvement of sarcoidosis. If the pituitary-hypothalamic axis is affected, endocrine studies should be done. In recent years, F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) imaging have been used to evaluate for neurosarcoidosis. F-18 FDG PET/CT is gaining popularity in patients with suspected systemic sarcoidosis, especially with pulmonary or cardiac involvement. It can provide valuable information to the site of involvement by the disease and selection of more surgically accessible sites for biopsy.
If the diagnosis remains uncertain, biopsies of the meninges, brain or spinal cord may be indicated. However, biopsies of the skin, lymph node, and lung are less risky and thus, are more preferred. A biopsy may also be considered for patients who do not respond to therapy.
Given the inflammatory process, corticosteroids are the main treatment for neural sarcoidosis. For facial nerve palsy or aseptic meningitis, prednisone is given every day for 2 weeks usually. In cases of meningeal, parenchymal mass lesion or myopathy or neuropathy, prednisone should be given for at least 4 weeks. For deteriorating patients, intravenous (IV) methylprednisolone is given for 3 days followed by prednisone for 2 to 4 weeks. The steroid dose should be tapered over several months with follow up by a neurologist every 3 to 6 months.
Immunosuppressants may also be considered, such as cyclosporine, methotrexate, and cyclophosphamide.
Other differentials to consider for neurosarcoidosis include primary brain tumors, toxin ingestion, neuropathies secondary to monoclonal proliferation or paraproteinemic neuropathy, paraneoplastic neuropathy, vitamin deficiency, leptomeningeal carcinomatosis, multiple sclerosis, central nervous system (CNS) lymphoma, or autoimmune conditions like systemic lupus erythematosus.
Neurosarcoidosis may present as either a monophasic illness, a relapsing-remitting course, or as a progressive disease with episodes of deteriorations. It is not well known what the long-term effects of neurosarcoidosis are. Usually, patients with facial nerve palsy or other cranial mononeuropathies will improve. In contrast, cases with aseptic meningitis or meningeal/parenchymal mass lesions have a longer course. Hypothalamic vegetative symptoms rarely resolve although may respond to treatment.
Encephalopathy/vasculopathy tends to have a relapsing-remitting course with deterioration. Cases with hydrocephalus may either be asymptomatic or cause rapid deterioration. Remissions are possible in peripheral neuropathy and myopathy cases, however, the course usually is chronic and progressive.
With a diagnosis of sarcoidosis, physicians should be careful to monitor the signs and symptoms of neurosarcoidosis, with the most common symptom being cranial neuropathy involving the facial nerve. However, although most cases resolve, it is important to provide follow-up care to monitor for evolving symptoms. Treatment involves steroids to stop the inflammatory response caused by systemic sarcoidosis.
An interprofessional approach to neurosarcoidosis is recommended.
Cases of neurosarcoidosis require an interprofessional effort because the disorder has diverse presentations and has no specific test to make a diagnosis. Given the systemic involvement associated with neurosarcoidosis, a variety of specialists should be consulted such as rheumatology, endocrinology, and pulmonology. Neurosurgery may be consulted as well for resection of CNS masses. However, biopsy/excision procedures that involve the CNS can be associated with severe consequences, and remain a treatment of last choice. Thus, resection should be deferred, unless the mass continues to enlarge after immunosuppression. For cases with hydrocephalus, a ventriculoperitoneal shunt may be placed, albeit the risk of infection. Patients on prolonged steroids may benefit a dietician consult to manage weight gain and to develop an exercise program and reduce bone loss. All patients started on corticosteroids need to be monitored for adverse effects by the pharmacist. As soon as symptoms subside, rapid tapering of the drug is recommended.