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Lambert-Eaton myasthenic syndrome

Myasthenia gravis

Dermatomyositis, polymyositis

Acute necrotizing myopathy

Carcinoid myopathies Myotonia

Cachectic myopathy Stiff-person syndrome

Data from Posner JB: Neurologic Complications of Cancer. Philadelphia, F. A. Davis, 1995.

neuronal phenotype. The mechanism for the inflammatory infiltrates, which consist of B cells, CD4+ and CD8+ lymphocytes, and macrophages, remains to be elucidated.

Epidemiology and Risk Factors. All small cell lung cancers with or without paraneoplastic symptoms express the Hu antigen, and 16 percent of patients with small cell lung cancer but lacking neurological dysfunction develop low titers of anti-Hu antibody. There is no overlap between the titers of anti-Hu antibodies in small cell lung cancer with paraneoplastic encephalomyelitis and sensory neuronopathy (average titer, 4592 U/ml) and those without neurological symptoms (average titer, 76 U/ml). All patients with low titers of anti-Hu antibody had the tumor confined to the thorax at diagnosis. In contrast, more than 50 percent of patients with small cell lung cancer without the anti-Hu antibody had systemic metastases at diagnosis. These findings, and the tendency of small cell lung cancer from patients with paraneoplastic encephalomyelitis and sensory neuronopathy to remain localized and undetectable until autopsy, suggest that the antitumor immune response contributes to the more indolent course of this neoplasm. d

Clinical Features and Associated Findings. Paraneoplastic encephalomyelitis with inflammatory infiltrates occurring throughout the neuraxis is described in a number of different syndromes all associated with small cell lung cancer.

Limbic encephalitis typically due to lymphocytic infiltration

and neuronal loss within the temporal lobes initially manifests as anxiety and depression, then progresses to loss of recent memory, agitation, confusion, hallucinations, behavioral abnormalities, hypersomnia, generalized or partial complex seizures, and progressive dementia. y Similarly, any level of the brain stem may be impaired with signs and symptoms reflective of that level of involvement. Involvement of the medulla oblongata produces nausea, vomiting, vertigo, nystagmus, ataxia, and bulbar palsy. Less commonly, disorders of eye movements occur when the midbrain or pons is involved. Extrapyramidal syndromes including parkinsonism, dystonia, respiratory abnormalities, deafness, and myoclonus of the bronchial musculature have been observed. y

When paraneoplastic cerebellar degeneration develops in patients with small cell lung cancer it is usually a minor component of a more widespread paraneoplastic encephalomyelitis and sensory neuronopathy. Paraneoplastic cerebellar degeneration as an isolated or predominant syndrome may occur in patients with small cell lung cancer with or without Hu antibody. Paraneoplastic cerebellar degeneration with Hu antibody is distinguished from that without Hu antibody by a female predominance, frequent association with paraneoplastic sensory neuronopathy, and neurological death. Progressive neurological deficits eventually plateau at the stage of severe affliction.

Evaluation and Differential Diagnosis. Before the era of neuroimaging the diagnosis of many paraneoplastic neurological syndromes was delayed or made at autopsy. Typically, in paraneoplastic encephalomyelitis pathological examination reveals predominant perivascular lymphocytic inflammation within the gray matter and overlying meninges in addition to neuronal loss, gliosis, and wallerian degeneration. The pathology of paraneoplastic encephalomyelitis and sensory neuronopathy is characterized by perivascular and parenchymal inflammatory infiltrates consisting of Hu-specific B and T lymphocytes, macrophages, and microglia. The trigger for these inflammatory infiltrates is unknown but is postulated to be circulating activated Hu-specific T lymphocytes; the resulting breakdown of the blood-brain barrier and intrathecal synthesis of anti-Hu antibody may then add to the pathology. y White matter changes are uncommon. Limbic encephalitis shows prominent involvement of the amygdala and neuronal loss within the pyramidal layer of the hippocampus with associated gliosis. MRI is either normal or can reveal T2-weighted signal abnormalities with mass effect within the mesial temporal structures in patients with limbic encephalitis. In patients with encephalitis involving the brain stem, atrophy of affected structures occurs over time.

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