Low skin temperatures indicate autonomic function impairments

Hands and feet of Rett patients have lower temperatures than people without the disease

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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An illustration of hands.

The hands and feet of people with Rett syndrome have a lower skin temperature than people without the disease, correlating with impairments in the autonomic nervous system, a study reports.

Skin temperature was measured using infrared thermal imaging (IRT), which uses infrared radiation, not visible to the human eye. The autonomic nervous system regulates involuntary body processes including heart rate, blood pressure, respiration, and digestion.

“As clinical trials are currently underway, identifying objective measures that can be used to supplement the clinical rating scales that often serve as primary outcomes is an important goal for RTT [Rett] and other neurodevelopmental disorders,” the researchers wrote in “Preliminary assessment of the reliability and validity of infrared skin temperature measurements in Rett syndrome,” which was published in the Journal of Intellectual Disability Research.

Rett syndrome is chiefly caused by mutations in the MECP2 gene, which codes for a protein of the same name. This protein regulates the activity of other genes and has an important role in brain development and function.

Patients commonly show impairments in the autonomic nervous system, and cold and discolored hands and feet are common. IRT has been used to evaluate hand and foot temperature in people with nerve damage associated with diabetes and Raynaud’s phenomenon, a condition wherein the fingers and toes become numb and cold in response to low temperatures or stress.

IRT’s potential to assess autonomic function in Rett patients has remained untested, causing a team led by researchers at the University of Minnesota, Minneapolis, to use it to evaluate hand and foot temperatures over time in 26 girls and women (age range, 5-39) with Rett syndrome due to MECP2 mutations. A group of 17 age-matched females without known intellectual, developmental, or neurological disorders served as controls. The Rett group was, on average, two months younger than the controls.

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Evaluating skin temperatures, disease severity, autonomic function

The team also evaluated the link between skin temperature, disease severity, and autonomic symptoms reported by caregivers.

Participants were asked to avoid vigorous physical activity in the two hours before the thermal measurement, which was conducted in a climate-controlled room. They waited in the room for 15 minutes without shoes and socks before thermal images were acquired.

To assess the stability and reliability of the skin temperature measurements, the researchers conducted a first test and then re-tests within three and 12 months. Results showed thermal imaging of the feet was less reliable than the hands, and lowest comparing left to right.

Compared to controls, Rett syndrome patients showed lower average hand temperatures, a mean of 31 C versus 32.7 C (87.8 F vs. 90.9 F) and lower feet temperatures — a mean 27.3 C versus 30.4 C (81.1 F vs. 86.7 F). Large bilateral (left to right) differences for hands and feet were more common among Rett patients.

When assessing how these measures correlated with the groups, the researchers found bilateral foot temperature differences showed a possible association with age in Rett patients only.

Rett clinical severity scores showed a positive correlation with bilateral foot temperature differences. This indicates that increased severity was linked with greater temperature differences between the feet.

Clinical severity showed a negative correlation with maximum foot temperatures, indicating more severe Rett cases have lower maximum temperatures.

The severity of autonomic symptoms was evaluated with a clinical questionnaire developed by local pediatric neurologists. Symptoms were scored from 0 (occurring never or rarely) to 3, occurring several times a week or daily.

Autonomic symptom scores were negatively correlated with the temperature (average and maximum) of hands and feet, but no link was found with bilateral differences. This suggests better autonomic function is linked with higher temperatures.

The severity of gross motor impairment was linked with temperature differences between the feet, while the severity of scoliosis (a sideways curvature of the spine) and kyphosis (an exaggerated, forward rounding of the upper back) were negatively associated with hand temperature and positively with the degree of bilateral foot temperature differences.

The researchers didn’t find any relation between epilepsy severity or breathing dysregulation and temperature measurements.

These findings “suggest that hand and foot temperature measure may have potential as biomarkers of autonomic dysfunction in RTT,” the researchers wrote.