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Case History

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Image not available. A 65-year-old woman with stage II ovarian cancer and hypothyroidism is admitted onto the acute oncology ward with a five-day history of progressive nausea, gait instability and oscillopsia. The patient does not drink alcohol and her only medication is thyroxine replacement therapy. On examination she manifests a downbeat nystagmus, past pointing, dysdiadochokinesia, and both truncal and gait ataxia.

What is the differential diagnosis?

What investigations would you do or request?

What is the treatment and prognosis?

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Background

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What is the differential diagnosis?

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Image not available. The signs and symptoms are suggestive of a cerebellar lesion. In the context of a person with a known malignancy, cerebellar metastases and paraneoplastic syndromes would be high on your list of differentials. Other conditions to consider include vascular (infarction/ischaemia), metabolic causes, medications (for example anticonvulsants) and thyroid dysfunction. In the context of patients with known cancer, practitioners should be cognisant of cerebellar insults secondary to certain types of chemotherapy, such as cytarabine and fluorouracil.

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What investigations would you request?

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Urgent neuroimaging is required to exclude a cerebellar mass. Magnetic resonance imaging (MRI) is more sensitive than computed tomography (CT) in detecting lesions within the cerebellum and brainstem, and should be requested if the initial CT scan is negative. Routine blood tests, including thyroid function, should be taken. Hypothyroidism is a rare, albeit treatable, cause of cerebellar dysfunction. Vitamin B and E levels should also be measured because deficiencies may interfere with cerebellar function.

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Image not available. Both the laboratory and radiological investigations fail to reveal an abnormality to explain the patient's cerebellar signs and symptoms.

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What is the most likely diagnosis?

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The most likely diagnosis is a paraneoplastic syndrome affecting the cerebellum, in particular paraneoplastic cerebellar degeneration (PCD). As a consequence, paraneoplastic biomarkers should be measured in the patient's serum.

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What are paraneoplastic syndromes?
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By definition, paraneoplastic syndromes are a heterogeneous group of neurological disorders that are associated with systemic cancer, but not by the cancer per se or side effects of its treatment. Although not completely understood, it is conjectured that these syndromes arise as result of an immunological response directed against shared antigens (in particular the nervous system) that are ectopically released by the tumour.1 A suggestion has been made that self-antigens may be processed differently in cancer cells, thus inciting a T-cell response.2

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It is noteworthy that paraneoplastic syndromes may arise from a non-immune, pathophysiological basis. An example is the release of hormones by a tumour, such as parathyroid hormone-related peptide (PTHrP) leading to hypercalcaemia.

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Numerous onconeural antibodies have been identified. Antibodies that have been classified as 'well characterized' are summarized in Table 34.1. The presence of any of these antibodies in a patient's serum is sufficient to define them as harbouring a paraneoplastic ...

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