More Research Needed on Early FAP Detection by Nailfold Capillaroscopy
Non-invasive technique images tiny blood vessels in finger nailbeds
Larger studies are needed to back the use of nailfold capillaroscopy — a non-invasive technique for imaging tiny blood vessels in the fingers — for the early detection of familial amyloid polyneuropathy (FAP), a new report says.
Nailfold capillaroscopy, known as NFC, allows researchers to image blood vessels found in the nailbeds to investigate microcirculation in the body. Scientists have suggested that the technique could help in a sooner diagnosis of FAP — a type of hereditary ATTR amyloidosis, or ATTRv amyloidosis — and, in turn, allow earlier treatment.
“From the therapeutic perspective of ATTRv amyloidosis, … early treatment is effective in preventing irreversible damage and poor quality of life,” the team wrote.
The report, “A pilot study of nailfold capillaroscopy in hereditary transthyretin amyloidosis” was published in the journal Scientific Reports.
FAP is a rare progressive disease caused by genetic mutations in the TTR gene, which provides instructions for making a protein called transthyretin. These mutations lead to the production of an abnormal version of the protein that accumulates in amyloid deposits across several tissues, particularly nerves, causing damage.
Although the exact mechanisms underlying nerve damage in FAP are still not fully understood, it has been hypothesized that microangiopathy — a condition that causes small blood vessels to become damaged — may play a role.
NFC is a non-invasive imaging technique that can be used to detect abnormalities in the small blood vessels, called capillaries, that are found in nailbeds. It mainly has been applied to rheumatic diseases, such as scleroderma, but recent studies have noted its potential use in other diseases characterized by small blood vessel abnormalities.
Now, a team led by researchers at Konkuk University Medical Center, in Seoul, South Korea, conducted a retrospective cross-sectional study to assess whether NFC might be useful to detect such abnormalities in FAP patients.
In total, they analyzed data from eight patients with FAP and one asymptomatic carrier — altogether, six men and three women, with a mean age of 54. Asymptomatic carriers are people who harbor a FAP-causing mutation, but have no overt disease symptoms. All of the patients had been followed at a single clinical center in Korea from April 2017 to December 2020, and had a mean disease duration of 7.5 years.
The patients were treated with either Onpattro (patisiran) or tafamidis, sold as Vyndaqel, among other brand names.
According to NFC results, all patients showed abnormalities in their nail capillaries, including having more dilated blood vessels and a decrease in their number. Changes in the architecture of capillary networks also were seen.
Notably, however, the asymptomatic carrier had the most severe form of impairment, while FAP patients with longer disease duration had fewer alterations to their capillary network.
According to researchers, these findings suggest that additional risk factors other than TTR gene mutation, such as smoking, could affect NFC results.
Despite these findings, researchers noted this was a small pilot study and that “further studies with a larger number of subjects will be needed to determine the use of NFC as an early detection tool [for FAP].”
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