Tests used to assess sensitivity to heat and cold may help diagnose patients with familial amyloid polyneuropathy (FAP) earlier as well as track their improvement after liver transplant, a case study suggests.

The study, “Evidence of neurophysiological improvement of early manifestations of small-fiber dysfunction after liver transplantation in a patient with familial amyloid neuropathy,” appeared in the journal Clinical Neurophysiology Practice.

Early diagnosis of  transthyretin FAP (TTR-FAP) is vital for patients to promptly begin appropriate therapies. Liver transplant is among the most effective ways to stop the disease from progressing, since the liver is the organ that produces  TTR protein — the underlying cause of TTR-FAP when mutated.

The most common mutation in the TTR gene results from an amino acid substitution in position 30 in the gene sequence, identified as Val30Met.

In this case report, researchers at Spain’s University of Barcelona discuss how using psychophysical and sensory methods may help detect the onset of polyneuropathy.

A 29-year-old woman was found to carry the TTR gene Val30Met mutation in 2008, but remained an asymptomatic carrier until 2012. She then began experiencing a burning or prickling sensation (paresthesia), accompanied by hyperalgesia, or increased sensitivity to pain, in both legs.

She visited the clinic three months after the onset of symptoms, but showed normal strength, tendon jerks and sensation to touch and position during her physical examination. However, she also displayed reduced sensation to warmth and coldness in her feet.

Researchers performed neurophysiological and psychophysical tests, including those to determine her threshold for heat, heat pain, cold and cold pain, as well as her ability to detect changes in temperature throughout an amplitude range test. These tests were performed seven months later, and right before she had a liver transplant.

After the transplant, she gradually improved, reaching a complete remission of her sensory impairments. She recovered her thermal sensation.

Follow-ups two and four years after her liver transplant showed that the patient regain an asymptomatic state, with the exception of occasional episodes of incontinence and as well as postural hypotension, a drop in blood pressure after three or more minutes of standing.

The authors concluded that this provides “more evidence in favor of the importance of early diagnosis and the potential for recovery if neurological damage remains within limits.”