A case report suggests that Friedreich’s ataxia can manifest as abnormal voluntary eye movements, rather than the typical loss of gait and limb control. To reduce the risk of misdiagnosis, researchers behind the report urge neurologists to bear in mind that the symptoms of the disease can vary widely, possibly including atypical features.
The study, “Early-Onset Friedreich’s Ataxia With Oculomotor Apraxia,” was published in the journal Acta Medica Iranica.
Oculomotor apraxia — the reduced or lost ability of voluntary eye movements — most often is a feature of another type of ataxia, called ataxia with ocular motor apraxia type 1 (AOA1). This condition also is linked to a range of abnormal laboratory measures, including high levels of cholesterol and low levels of the protein albumin in the blood.
In their report, researchers at Tehran University of Medical Sciences describe two sisters who appeared to have a mix of the two ataxias. One girl was 13 years old when first examined, but her mother had noticed balance problems already when the child was five.
Exams revealed that she walked unsteadily, with both balance and coordination difficulties. Her handwriting also was affected. She had no problems with her eyesight, hearing, or mental state. She did, however, have obvious oculomotor apraxia.
The girl had a normal muscle tone and normal sensation responses, but failed to put her finger on her nose when asked to perform the task. She also had problems with tandem walking.
A brain scan showed significant neuro-degeneration in her cerebellum, but the majority of laboratory tests came back normal. Tests of her nerve cell function showed she had damaged axons (the projections of neurons) outside the central nervous system.
Her younger sister was 10 years old when she started experiencing similar symptoms. Her balance and coordination problems were of a different kind, and she had difficulties maintaining her balance while sitting.
Since AOA1 is commonly diagnosed in children, neurologists first believed the girls had this type of ataxia. But the lack of abnormal measures of cholesterol, albumin, and other AOA1-related findings made them reconsider, and the girls were diagnosed with Friedreich’s ataxia.
“Therefore, neurologists should bear in mind that clinical presentations of FRDA may vary widely from the classical phenotype of gait and limb ataxia to atypical manifestations such as oculomotor apraxia,” the researchers concluded.
Physicians could not set a genetic diagnosis since they did not have access to blood samples from the patients. So, particularly in cases where genetic analysis is not possible, laboratory tests can be used to discriminate between the two conditions.