Loss of Smell Linked to Disease Severity
Sensitivity to smell is reduced in people with Sjögren’s syndrome, compared with healthy controls, and appears to be linked to the severity of the disease, a new study reports.
The study, “Olfactory impairment in patients with primary Sjogren’s syndrome and its correlation with organ involvement and immunological abnormalities,” was published in Arthritis Research & Therapy.
Sjögren’s syndrome is an autoimmune condition that arises when the immune system attacks glands that produce secretions, leading to severe dryness in the affected areas.
The disease is classified as either primary or secondary Sjögren’s syndrome depending on whether it exists on its own or with another autoimmune disease, such as rheumatoid arthritis or lupus.
Autoimmune conditions seem to predispose patients to losing some or all their ability to smell. Yet, the evidence for smell abnormalities in people with primary Sjögren’s syndrome is contradictory, which may be related to the lack of comprehensive tests for assessing loss of smell.
A team of scientists at Nanjing Drum Tower Hospital, in China, now sought to clarify existing evidence by using comprehensive computerized smell tests to measure smell sensitivity in people with primary Sjögren’s syndrome.
They also expanded existing scientific evidence by investigating whether smell sensitivity could predict disease severity and if it was related to the levels of autoantibodies (antibodies to self-proteins), symptoms in other organs, and type of treatment.
A total of 52 patients (three males, 49 females) and 52 healthy controls, matched in age and sex, were included in the analysis.
The participants reported their sense of smell on a scale of 0 to 10 (0 meant complete loss of smell perception and 10 meant an excellent perception of smell). Also, researchers assessed their sense of smell with a computerized test that measured three parameters: odor threshold (the ability to detect a smell after successive dilutions), odor identification, and odor memory.
Participants received a score for each parameter, which were summed and referred to as the TIM score (threshold + identification + memory). The TIM score ranged from 1 to 63.5 points.
Compared to healthy controls, people with Sjögren’s had a significantly lower self-reported sense of smell — with a mean score of 6.09 vs. 8.25 in controls. Also, more patients than controls experienced a complete loss of smell (13.5% vs. 0%) and a reduced ability to smell (19.2% vs. 11.5%).
Smell threshold, smell identification, and smell memory were significantly lower in people with Sjögren’s compared with healthy controls. Their mean TIM score was 40.91, which was significantly lower than in healthy controls (50.49).
To investigate if there was a link between smell sensitivity and clinical assessments, the researchers used three measures of disease activity: the European League Against Rheumatism (EULAR) Sjögren’s Syndrome Patient Reported Index (ESSPRI); EULAR Sjögren’s Syndrome Disease Activity Index (ESSDAI); and erythrocyte sedimentation rate (ESR).
They found that higher ESSDAI scores were associated with a worse smell threshold, while ESSPRI was associated with a worse smell threshold, smell identification, and smell memory.
Patients with other symptoms, including dryness, fatigue, and limb pain, also experienced worse TIM scores overall, with the kind of smell dysfunction depending on the exact symptom.
Additional results showed that people with thyroid abnormalities had significantly reduced smell identification, smell memory, and TIM scores than those without. Furthermore, people with antinuclear and anti-SSA antibodies had significantly lower smell threshold and TIM scores than people without autoantibodies.
Finally, people taking glucocorticoids tended to have lower smell threshold scores than those not taking glucocorticoids. Treatment with hydroxychloroquine and immunosuppressants did not affect smell sensitivity.
“In conclusion, our results demonstrated a significant reduction in the olfactory (smell) abilities of primary Sjögren’s syndrome patients, which correlated with disease activity,” the researchers wrote.
“These data,” they added, “could have useful value in the diagnosis of primary Sjögren’s syndrome.”