Fewer capillaries in hands may contribute to scleroderma bone loss
Study: Low bone density associated with several disease features
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The loss of capillaries in the hands may directly contribute to local bone loss in people with systemic sclerosis (SSc), a study revealed for the first time.
Data showed that SSc patients with fewer capillaries at the base of the fingernails had lower bone density in the hands. Such low bone density was associated with several SSc features, including skin and gastrointestinal involvement, as well as reduced grip strength.
“For the first time, hand local bone status was found significantly associated with hand/fingers [vascular] damage in SSc patients,” researchers wrote. “At the same time, the results of the [statistical] model reinforced the role of capillary loss as a potential predictor of hand bone quality in SSc patients.”
The study, “Hand bone densitometry associates with nailfold capillaroscopic severity of microvascular damage in systemic sclerosis: a pilot study,” was published in Clinical and Experimental Rheumatology.
Studies show up to 58% of SSc patients have low bone mineral density
SSc, also called scleroderma, is an autoimmune disease characterized by excessive production of collagen, the main protein of connective tissue. This leads to skin hardening (fibrosis) and vascular damage that can affect internal tissues and organs.
Studies show that up to 58% of SSc patients have low bone mineral density (BMD), a measure of bone strength. This can increase the risk of osteoporosis, a condition marked by deteriorating bone structure and an increased risk of fractures.
The microvascular damage, or damage to the smallest blood vessels called capillaries, that is characteristic of SSc reduces oxygen supply to tissues, which may, in turn, harm bone tissue.
Researchers set out to examine, for the first time, whether the severity of microvascular damage in the hands is related to bone density as measured in those same hands.
“SSc is associated with severe microvascular impairment and diffuse bone loss, however, the link between altered microcirculation and local bone integrity remains unclear,” they wrote.
Patients with fewer capillaries had lower bone density
The study enrolled 32 SSc patients from the rheumatology division at the University of Genova in Italy. Their mean age was 61.7 years, nearly all (94%) were women, and their mean disease duration was 10 years. The team also examined 27 healthy individuals matched for age and sex.
Roughly half (47%) of the patients had diffuse cutaneous SSc (dcSSc, the subtype with more widespread skin involvement), and the rest had limited cutaneous SSc (lcSSc). At the time of the study, 43.7% of the participants already had a diagnosis of osteoporosis, and 15.6% had experienced osteoporotic fractures.
Microvascular status was assessed using nailfold videocapillaroscopy (NVC), a technique that uses a video microscope to examine the capillaries visible at the base of the fingernails. Bone mineral density was measured using DXA, a standard bone scanning technique.
An examination of the data revealed a significant positive correlation between capillary density (number of capillaries per mm) and hand BMD, meaning that patients with fewer capillaries had lower bone density. The findings applied to both hands.
A statistical analysis confirmed this association after accounting for factors such as age, sex, body mass index (a screening tool that uses height and weight to estimate body fat), history of osteoporosis, grip strength, immunosuppressive therapy, and osteoporosis treatment.
Findings back video technique as biomarker of systemic bone status
Left-hand BMD was also significantly lower in patients with the “late” NVC pattern, reflecting severe vascular damage. Similarly, a low right-hand BMD was correlated with more structural disorganization of capillaries. Capillary density also correlated with BMD in the femoral neck (hip joint), total femur (upper leg bone), and the spinal column, “further reinforcing the role of nailfold videocapillaroscopy as a biomarker of systemic bone status,” the team noted.
SSc patients had significantly lower left-hand BMD than healthy individuals, a difference that remained significant after adjustment for age, sex, body mass index, and history of osteoporosis. Similarly, SSc patients had significantly lower vertebral and femoral BMD.
Several SSc disease characteristics were associated with lower hand BMD. Those with dcSSc had lower left-hand BMD than those with lcSSc. A higher modified Rodnan skin score, a measure of skin thickness reflecting more extensive fibrosis, correlated with a lower left hand BMD.
The results of this detailed investigation suggest that SS-related microvascular insufficiency, as detected by NVC, may contribute to enhancing local bone damage and loss. For the first time, local bone status of the hand was found to be significantly associated with hand/finger microvascular damage.
Higher left-hand BMD showed a modest correlation with more grip strength measured by a dynamometer, though this finding was not replicated in the right hand.
The lack of a correlation between BMD and grip strength in the right hand “may be attributed to the protective effect of daily mechanical loading on the dominant hand, which might mask the underlying bone loss observed in the non-dominant limb,” the researchers wrote.
Gastrointestinal involvement was also correlated with low left-hand BMD and bone mineral content, the total amount of mineral in the bone. Likewise, patients positive for anti-Scl70 antibodies (associated with more aggressive disease) had significantly lower left-hand BMD, whereas those positive for anti-centromere antibodies (associated with more limited disease) had relatively higher left-hand BMD.
No significant associations were found between hand BMD and disability, as measured by the Health Assessment Questionnaire, or between hand BMD and hand movement, as indicated by the Hand Mobility in Scleroderma test.
The researchers noted that about half of the SSc patients were already receiving osteoporosis treatments at the time of the study, which may have influenced the BMD data.
“The results of this detailed investigation suggest that SSc-related microvascular insufficiency, as detected by NVC, may contribute to enhancing local bone damage and loss,” the researchers concluded. “For the first time, local bone status of the hand was found to be significantly associated with hand/finger microvascular damage.”
