Subacute cerebellar degeneration (SCD) is characterized by the deterioration of the area of the brain concerned with muscle coordination and balance (the cerebellum). Less frequently, the area involved may include the area connecting the spinal cord to the brain (the medulla oblongata, the cerebral cortex, and the brain stem). There are two types of subacute cerebellar degeneration: paraneoplastic cerebellar degeneration, which sometimes precedes the diagnosis of cancer, and alcoholic or nutritional cerebellar degeneration, caused by a lack of the vitamin B-1 (thiamine). These two types share symptoms but not the same cause.
Common symptoms of subacute cerebellar degeneration include:
(1) weakened muscle coordination (ataxia) of the limbs (especially of the arms in paraneoplastic cerebellar degeneration, and of the legs in alcoholic or nutritional cerebellar degeneration);
(2) problems in articulation of speech (dysarthria), which are especially noticeable in paraneoplastic cerebellar degeneration;
(3) difficulty in swallowing (dysphagia);
(4) loss of reason (dementia); this occurs in approximately half the patients with paraneoplastic cerebellar degeneration;
(5) involuntary rapid movements of the eyeball in a horizontal or vertical direction (nystagmus); as well as double-vision (diplopia), vertigo (dizziness), paralysis of the eye muscles (ophthalmoplegia), and difficulty in walking if the patient has alcoholic/nutritional cerebellar degeneration.
In addition, patients with SCD lose many of a particular kind of nerve cell (Purkinje cells) throughout the cerebellum. CAT scans may show enlargement of the area of the brain between the spinal cord and the rest of brain (fourth ventricle) as well as areas of the cerebellum. Examination of cerebrospinal fluid may show a high volume of lymph cells (white blood cells formed in lymphoid tissue) and an elevated protein level.
The causes of subacute cerebellar degeneration are as follows.
Paraneoplastic cerebellar degeneration may be an autoimmune disorder. Autoimmune disorders are caused when the body’s natural defenses against “foreign” or invading organisms (e.g., antibodies) begin to attack healthy tissue for unknown reasons. In cases in which there is an underlying cancer, the individual’s immune system may be responding to its presence by stimulating the body’s natural cancer-fighting mechanisms (T-cells, which are a type of white blood cell) to attack normal cells in the nervous system.
Alcoholic/nutritional cerebellar degeneration is associated with thiamine deficiency. Secondary thiamine deficiency results from increased requirements for thiamine, and from impaired absorption or impaired utilization of the vitamin. Alcoholics tend to eat poorly and may not get enough thiamine- containing foods. Also, they seem to absorb or utilize the vitamin less efficiently and, therefore, may require larger than normal amounts of thiamine.
In paraneoplastic cerebellar degeneration, the average age of onset is 50, with males affected more often than females. This form of cerebellar degeneration may precede cancer. Alcoholic or nutritional cerebellar degeneration affects alcoholics and people with thiamine deficiency. It is not related to cancer and is more common than the paraneoplastic type.
Paraneoplastic cerebellar degeneration may improve after successful treatment of the underlying cancer. For alcoholic/nutritional cerebellar degeneration, thiamine is given along with other B vitamins, usually relieving the condition if the patient stops drinking alcohol and resumes a normal diet.
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