A non-invasive test that measures nerve conduction through surface electrodes may help diagnose polyneuropathy — damage to multiple nerves outside the brain and spinal cord — in patients with Sjögren’s syndrome, a study suggests.
The study, “Polyneuropathy and the sural/radial sensory nerve action potential ratio in primary Sjögren’s syndrome,” was published in the journal Neurological Research.
While damage and dryness of certain glands are the most common manifestation of Sjögren’s, patients may have extraglandular manifestations involving the kidneys, lungs, muscles, and the nervous system.
A large number of studies have reported that neurological manifestations are seen in about 20% of Sjögren’s patients, most commonly involving damage to the peripheral nerves — those that send sensory and motor information from the brain and spinal cord to the rest of the body. As a result, patients experience a sensation of numbness, coldness, or pain in their extremities.
However, the lack of a standardized diagnostic approach has made it difficult to determine the exact prevalence of polyneuropathy, with studies reporting variable rates of less than 2% to more than 60%.
Thus, researchers set out to use a non-invasive test that measures nerve conduction in the legs and arms — called the sural/radial ratio (SRAR) — to determine the prevalence of polyneuropathy in Sjögren’s syndrome patients. SRAR is used as a marker for early nerve damage, where a value of 0.4 or less corresponds to a positive diagnosis, but its value in Sjögren’s has not been addressed until now.
The study recruited 52 women with primary Sjögren’s and 50 healthy women as controls. All patients were being treated with hydroxychloroquine, 10% were using methotrexate, 10% were on azathioprine, and one-third (33%) were also using steroids.
Researchers found that three patients had axonal polyneuropathy, which initially manifests as numbness or weakness on the toes and feet, slowly progressing up the leg — what’s known as a “stocking-glove” distribution of symptoms. The patients also had no ankle tendon reflex.
Of the patients, 22 experienced pain and 16 had numbness, burning, tingling, or stabbing sensations in the upper or lower limbs. A total of 13 patients had reduced or absent ankle reflexes.
SRAR was performed in 49 patients and in the 50 healthy women. SRAR values were lower than 0.4 in 20.4% of patients and in 6% of controls — a statistically significant difference. However, the presence of anti-Ro and anti-La antibodies — characteristic of Sjögren’s — did not affect SRAR values, the researchers found.
But they did find a negative correlation among age, body mass index, and the presence of numbness or burning sensations with SRAR in the patient group. Essentially, this means that the patients experiencing numbness had lower SRAR values and were likely to have damage to the peripheral nerves.
“Based on this relationship, we think that SRAR has electodiagnostic utility in the early diagnosis of distal sensory neuropathy in [primary Sjögren’s syndrome],” the researchers wrote.
“We think that markers such as SRAR are important in the diagnosis of chronic process diseases such as pSS with multisystem involvement,” they concluded.