Magnetic resonance-guided focused ultrasound (MRgFUS) may become a promising treatment for chronic pain from musculoskeletal diseases and bone metastases, suggest Japanese researchers. A multi-institutional study published in the Sept. 2, 2019, edition of Pain Research and Management showed that MRgFUS reduced pain at the site of most severe tenderness in patients with bone metastases, lumbar facet joint osteoarthritis, and knee osteoarthritis.
Physicians at the Department of Orthopedic Surgery at the Kochi Medical School in Nankoku, Kochi, assessed the therapeutic effect of MRgFUS applied to locations of maximal tenderness in 40 patients by evaluating changes in pressure pain thresholds and pain. They recruited 10 patients with painful bone metastases in the ilium, sacrum, femur, scapula, and pubic bone, who had not responded to conventional palliative therapy. Although all patients had either osteolytic or osteoblastic lesions or both, bone surface structure in the treatment area was maintained. Eleven patients with chronic low back pain and 18 with chronic medial knee pain who had responded to conservative treatment for at least a 6-month period were also recruited.
MRI determined proper transducer placement, and sonication sessions lasted about 20 seconds, followed by a 90-second cooling period. The authors reported that a low-energy sonication was initially applied to ensure safety and accuracy, followed by therapeutic sonication. Proton resonance frequency shift thermometry was used for real-time monitoring each sonication location and temperature of tissues adjacent to the targeted area.
To the surprise of the researchers, who had expected the patients with bone metastases to achieve the greatest pain relief, response by all three groups was comparable. The researchers defined treatment response as a 50% or greater reduction in pain Numeric Rating Scale (NRS) scores. Seven days after treatment, 60% of bone metastasis patients, 64% of back pain patients, and 50% of knee pain patients responded to treatment. At one month, these percentages increased to 80%, 78%, and no change, respectively, in each group.
At 90 days, pain relief increased to 82% in back pain patients, and remained at 80% for bone metastasis patients. There was a decline to 67% in the patients with knee osteoarthritis.
NRS scores decreased dramatically for all patients. Pain pressure thresholds significantly increased for all three groups, as well.
The researchers attribute the lengthy pain reduction in metastasis patients to several factors. “First, the treatment causes denaturation of not only the sensory nerves but also the superficial part of the lesion itself,” they wrote. “Therefore, the treatment might prevent lesion expansion to some extent. Second, pain associated with bone metastases is not usually generated by joint motion, in contrast to that with osteoarthritis. Lastly, a large proportion of patients did not have rapidly progressing tumors.”
While acknowledging that the study focused on short-term pain reduction, the authors were impressed with the response to MRgFUS. “We found similar therapeutic effects for all three diseases. This study shows that the efficacy of the treatment in osteoarthritis is similar to that in painful bone metastases,” they wrote.
“Pain pressure thresholds began to increase significantly from an early stage. In both bone metastases and osteoarthritis, focal ablation of local hypersensitive nerve fibers seems capable of effectively reducing the level of pain experienced by the patient,” they concluded.
MRgFUS is effective for bone metastasis and osteoarthritis pain. Appl Radiol.