Case Report of a Rare Spinal Segmental Myoclonus Condition in Friedreich’s Ataxia Patient
Researchers at Sawai Man Singh Medical College in India recently reported a case of a Friedreich’s ataxia patient with an abnormal rare movement manifestation. The study was published in the journal SpringerPlus and entitled “Familial segmental spinal myoclonus: a rare clinical feature of Friedreich’s ataxia”.
Friedreich’s ataxia is a rare inherited neurodegenerative disease characterized by progressive damage of the nervous system with degeneration of the spinal cord and peripheral nerves that leads to muscle weakness, sensory loss, balance deficits and lack of voluntary coordination of muscle movements. Patients can also experience skeletal deformities, hypertrophic cardiomyopathy (disorder in which the heart muscle becomes abnormally hypertrophied) and diabetes mellitus. Disease onset usually occurs during childhood or adolescence and the disorder leads to progressive disability, dependence on a wheelchair and reduced life expectancy.
Friedreich’s ataxia is caused by a mutation in a gene called frataxin (FXN), more specifically by an expansion of guanine-adenine-adenine (GAA) trinucleotide repeats in the first intron (coding unit) of the FXN gene, which leads to a reduction in messenger RNA and the subsequent down-regulation of the frataxin protein. Normal FXN alleles contain less than 36 GAA repeats, whereas disease-causing alleles have expanded GAA repeats that can go up to 1,700. The length of the GAA repeat expansion is directly associated with disease severity.
In the study, researchers reported a case of a 19-year-old boy that had gradually developed a progressive neurologic illness that affected his gait, speech and caused scoliosis in the thoracic spine. There was no clinical history of fever, headaches, abnormal behavior, cognitive decline or seizures.
Upon physical examination, the patient was found to have thoracic scoliosis and pes cavus deformities. Low muscle tone (hypotonia), muscle wasting and weakness were observed in all four limbs. The patient experienced frequent involuntary, brief, jerky movements in his upper limbs that seemed to be worse in fatigue and mental stress situations. No involuntary jerk movements were observed during sleep. The patient’s pain, temperature and touch sensations were intact but vibration and joint position senses were impaired below the knees. Dysarthria (unclear articulation of speech) and truncal and limb ataxia (lack of voluntary muscular coordination) were also observed.
The patient’s blood tests and electrocardiography (ECG) were normal, and electroencephalogram (EEG) did not reveal epileptic activity. Myoclonic bursts in specific muscles were observed, which refers to sudden, shock-like, brief, jerky involuntary movements. Genetic analysis of the FXN gene revealed that the patient had an expansion of more than 66 GAA repeats.
Taken together, the results allowed a diagnosis of Friedreich’s ataxia with spinal segmental myoclonus (SSM), a rare movement disorder characterized by involuntary contractions of skeletal muscle groups innervated by a limited spinal cord region.
The patient had four siblings, and one of his younger brothers (12 years old) had similar clinical symptoms with progressive scoliosis, unsteadiness of gait and involuntary, jerky movement of the arms. The family received genetic counselling and the disorders and prognosis were explained. The patient initiated a high dose of coenzyme-Q for Friedreich’s ataxia symptoms along with physiotherapy in addition to clonazepam (0.5 mg twice a day) for his SSM condition. Unfortunately, there was no response to treatment. The patient is currently being closely monitored.
The team emphasizes that there are only very few case reports of abnormal involuntary movements in Friedreich’s ataxia patients. The authors believe that this might be the first case report of SSM in Friedreich’s ataxia, being a unique and rare manifestation of the disease.