What is (are) progressive external ophthalmoplegia ?
Progressive external ophthalmoplegia is a condition characterized by weakness of the eye muscles. The condition typically appears in adults between ages 18 and 40. The most common signs and symptoms of progressive external ophthalmoplegia are drooping eyelids (ptosis), which can affect one or both eyelids, and weakness or paralysis of the muscles that move the eye (ophthalmoplegia). Affected individuals may also have general weakness of the skeletal muscles (myopathy), particularly in the neck, arms, or legs. The weakness may be especially noticeable during exercise (exercise intolerance). Muscle weakness may also cause difficulty swallowing (dysphagia).  When the muscle cells of affected individuals are stained and viewed under a microscope, these cells usually appear abnormal. These abnormal muscle cells contain an excess of structures called mitochondria and are known as ragged-red fibers. Additionally, a close study of muscle cells may reveal abnormalities in a type of DNA found in mitochondria called mitochondrial DNA (mtDNA). Affected individuals often have large deletions of genetic material from mtDNA in muscle tissue.  Although muscle weakness is the primary symptom of progressive external ophthalmoplegia, this condition can be accompanied by other signs and symptoms. In these instances, the condition is referred to as progressive external ophthalmoplegia plus (PEO+). Additional signs and symptoms can include hearing loss caused by nerve damage in the inner ear (sensorineural hearing loss), weakness and loss of sensation in the limbs due to nerve damage (neuropathy), impaired muscle coordination (ataxia), a pattern of movement abnormalities known as parkinsonism, or depression.  Progressive external ophthalmoplegia is part of a spectrum of disorders with overlapping signs and symptoms. Similar disorders include other conditions caused by POLG gene mutations, such as ataxia neuropathy spectrum, as well as other mtDNA deletion disorders, such as Kearns-Sayre syndrome. Like progressive external ophthalmoplegia, the other conditions in this spectrum can involve weakness of the eye muscles. However, these conditions have many additional features not shared by most people with progressive external ophthalmoplegia.