Laboratory Studies
Serum and CSF paraneoplastic antibody panel are used to identify paraneoplastic etiology and detect autoimmune markers (eg, high levels of autoantibodies to glutamic acid decarboxylase [GAD-ab] [14] ).
Cerebrospinal fluid
Cell count, protein, glucose, oligoclonal bands, IgG synthesis rate, cytology, and PCR for herpes simplex virus and varicella zoster virus.
Assess for differential diagnoses involving the central nervous system.
Serum tumor markers
Carcinoembryonic antigen (CEA), cancer antigen 125 (CA-125), prostate-specific antigen (PSA).
Evaluate for an underlying malignancy.
Other tests
Other tests that may prove helpful for diagnosis include the following:
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Complete blood cell count with platelets - Monitor for infection, immunosuppression, anemia, or thrombocytopenia.
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Prothrombin time (PT)/activated partial thromboplastin time (aPTT) - Identify coagulopathies.
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Serum chemistries, including electrolytes and osmolarity - Monitor for associated electrolyte abnormalities or metabolic derangements.
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Toxicology screen - Identify a toxic etiology.
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Vitamin B 12 level - Rule out vitamin deficiency.
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Liver function tests - Evaluate hepatic causes of encephalopathy.
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Screening for infectious or hematologic etiologies - Selective evaluation of possible infectious or hematologic etiologies.
Imaging Studies
Head CT provides limited information regarding paraneoplastic encephalomyelitis (PEM) but allows for preliminary evaluation of differential diagnoses such as herpes simplex encephalitis or intracranial metastatic disease. Hypodensity on CT scan may be seen in chronic stages of PEM.
Brain MRI may help to rule out the differential diagnoses. Usually, MRI in a patient with PEM is unremarkable, although T2-weighted hyperintensity may be noted in mesial temporal lobes and associated limbic structures (see following image). Posterior thalamic T2 hyperintensity, or the "pulvinar sign [15] ," may be present. Contrast enhancement may be demonstrated with subsequent development of atrophy and gliosis, reflecting the dynamic evolution of inflammatory injury. MR spectroscopy of the brain may add further information.
Mesial temporal hyperintensity demonstrated on T2-weighted (left) and fluid-attenuated inversion recovery (FLAIR, right) MRI.
Positron emission tomography (PET) may illustrate hypermetabolism of limbic regions during the active phase of disease, supplanted by hypometabolism in the chronic phase. Whole body PET may also identify the primary lesion.
Myelography may demonstrate an enlarged spinal cord associated with inflammation.
The following studies may be done to identify an underlying malignancy:
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CT/MRI of the chest, abdomen, and pelvis
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Testicular ultrasonography [16]
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Mammography
Other Tests
Electroencephalography (EEG) may reveal focal temporal or diffuse paroxysmal sharp waves and spikes, and/or slowing.
Electromyography/nerve conduction studies of subacute sensory neuronopathy may reveal selective damage of sensory pathways with limited detection of H waves and preservation of motor nerve velocities and F waves. Studies of myelitis may exhibit motor denervation.
Procedures
Lumbar puncture is essential for determination of the CSF profile and detection of intrathecal paraneoplastic antibodies.
Diagnostic imaging modalities may help avoid the need for brain biopsy in some cases.
Histologic Findings
The neuropathologic findings in paraneoplastic encephalomyelitis (PEM) are typically more extensive than the degree of neurologic manifestations. Gross examination of the brain is usually unremarkable. Neuronal degeneration, gliosis, and an inflammatory infiltrate may be demonstrated throughout the brain. Perivascular and interstitial infiltrates are composed of B lymphocytes and cluster of differentiation 4 (CD4+) and CD8+ T lymphocytes, with microglial proliferation and neuronophagia. Limbic structures are particularly vulnerable, with prominent involvement of the hippocampus, amygdala, parahippocampus, cingulate cortex, insular cortex, and basal frontal lobes. Similar changes may be noted in the diencephalon, brain stem, deep cerebellar nuclei, spinal cord, dorsal root ganglia, sympathetic ganglia, and myenteric plexus.
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Paraneoplastic encephalomyelitis.
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Paraneoplastic encephalomyelitis.
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Mesial temporal hyperintensity demonstrated on T2-weighted (left) and fluid-attenuated inversion recovery (FLAIR, right) MRI.
