Amyloidosis is a disease resulting from abnormal protein deposits in extracellular tissue. The disease can be localized or systemic and can be further subclassified as primary, secondary, and familial. In primary amyloidosis, the protein fibrils form without a known cause. Secondary amyloidosis results from multiple myeloma or other chronic diseases that generate an abnormal amount of protein breakdown. Familial amyloidosis refers to a hereditary version of the disorder. Presentation is initially asym-ptomatic but proteinuria may be an early finding. Cardiac, dermatologic, gastrointestinal, and other organ systems show dysfunction depending on the location of the abnormal protein deposition. Any organ system in the body can be involved.
Neurologic involvement is usually of the peripheral nerves, the spinal nerve roots, and the autonomic ganglia, with the brain usually spared (116). Peripheral neuropathy in amyloidosis is found in 17% of patients. Cranial nerve involvement is rare in amyloidosis. Although cranial neuropathies are more common in familial amyloidosis, recent reviews have demonstrated cranial nerve involvement in primary amyloidosis (117). The facial nerve is rarely involved in cases of primary, secondary, and familial amyloidosis.
Although the mechanism of damage remains unknown, electromyographic studies have shown evidence of chronic partial denervation with amyloid deposits demonstrated in the perineurium (116). Some hypothesize that a progressive buildup of amyloid fibrils around cells results in injury. Amyloid deposits have been demonstrated to involve the facial nerve directly, with nearly complete replacement of the nerve (118).
Diagnosis is confirmed with biopsy demonstrating green birefringence of the abnormal protein using Congo red staining when viewed with a polarizing light. Serologic or urinary identification of homogeneous protein fibrils is also possible. Treatment with alkylating agent-based chemotherapy has had some success in amyloidosis. Clinical trials are underway for corticosteroid and a-interferon treatment. Colchicine may be beneficial in some forms of familial amyloidosis.
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