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A variety of nonmetastatic neurologic complications of malignant disease can be recognized. Metabolic encephalopathy due to electrolyte abnormalities, infections, drug overdose, or the failure of some vital organ may be reflected by drowsiness, lethargy, restlessness, insomnia, agitation, confusion, stupor, or coma. The mental changes are usually associated with tremor, asterixis, and multifocal myoclonus. The electroencephalogram is generally diffusely slowed. Laboratory studies are necessary to detect the cause of the encephalopathy, which must then be treated appropriately.

Immune suppression resulting from either the malignant disease or its treatment (eg, by chemotherapy) predisposes patients to brain abscess, progressive multifocal leukoencephalopathy, meningitis, herpes zoster infection, and other opportunistic infectious diseases. Moreover, an overt or occult cerebrospinal fluid fistula, as occurs with some tumors, may also increase the risk of infection. MRI or CT scanning aids in the early recognition of a brain abscess, but metastatic brain tumors may have a similar appearance. Examination of the cerebrospinal fluid is essential in the evaluation of patients with meningitis and encephalitis but is of no help in the diagnosis of brain abscess.

Cerebrovascular disorders that cause neurologic complications in patients with systemic cancer include nonbacterial thrombotic endocarditis and septic embolization. Cerebral, subarachnoid, or subdural hemorrhages may occur in patients with myelogenous leukemia and may be found in association with metastatic tumors, especially melanoma. Spinal subdural hemorrhage sometimes occurs after lumbar puncture in patients with marked thrombocytopenia.

Disseminated intravascular coagulation occurs most commonly in patients with acute promyelocytic leukemia or with some adenocarcinomas and is characterized by a fluctuating encephalopathy, often with associated seizures, that frequently progresses to coma or death. There may be few accompanying neurologic signs. Venous sinus thrombosis, which usually presents with convulsions and headaches, may also occur in patients with leukemia or lymphoma. Examination commonly reveals papilledema and focal or diffuse neurologic signs. Anticonvulsants, anticoagulants, and medications to lower the intracranial pressure may be of value.

Autoimmune paraneoplastic disorders occur when the immune system reacts against neuronal antigens expressed by tumor cells. The clinical manifestations depend on the autoantibody. Symptoms may precede those due to the neoplasm itself. Several distinct syndromes are common, including paraneoplastic cerebellar degeneration, limbic encephalitis, encephalomyelitis, anti-NMDA receptor-associated encephalitis, opsoclonus/myoclonus, sensory neuronopathy, retinopathy, and dermatomyositis.

Paraneoplastic cerebellar degeneration occurs most commonly in association with carcinoma of the lung, but also in breast and gynecologic cancers and Hodgkin lymphoma. Typically, there is a pancerebellar syndrome causing dysarthria, nystagmus, and ataxia of the trunk and limbs. The disorder is associated with anti-Yo, -Tr, -voltage-gated calcium channel (VGCC), and Zic antibodies. Treatment is of the underlying malignant disease. Limbic encephalitis, characterized by impaired recent memory, disturbed affect, hallucinations, and seizures, occurs in some patients with tumors of the lungs, breast, thymus, and germ cells. Associated antibodies include anti-Hu, -Ma2, -CV2/CRMP5, -voltage-gated potassium channel (VGKC), -leucine rich glioma inactivated 1 (LGI1), -contactin associated protein-like 2 (Caspr2), -dipeptidyl-peptidase-like protein-6 (DPPX), -AMPA receptor, -GABAA receptor, ...

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