Botulinum Toxin Type A for Ocular Pain in Chronic Relapsing Inflammatory Optic Neuropathy
Optic neuritis (ON) is a condition that can be quite challenging. Usually, it ends with one episode, but in 3% to 5% of patients, it recurs. Among these recurrent patients, those who test negative for multiple sclerosis or neuromyelitis optica (NMO) are diagnosed with chronic relapsing inflammatory optic neuropathy (CRION). This disease group, first named by Kidd et al, involves repeated inflammatory optic nerve inflammation on both sides, which worsens when steroids or immunosuppressants are discontinued. Early diagnosis is crucial as the risk of blindness is significant, and treatment focuses on preserving vision. However, many CRION patients also suffer from ocular pain, which shouldn’t be ignored.
The cervical sympathetic trunk (CST) is an important anatomical structure. All the sympathetic nerves of the face and neck pass through it. A cervical sympathetic block (CSB) is often used to control pain. When only a local anesthetic is used, the analgesic effect may be short-lived, but it can be prolonged with radiofrequency treatments. Botulinum toxin (BTX) administered to the lumbar sympathetic trunk has been reported to lengthen the analgesic period. So, could injecting BTX during CSB have a similar effect? This case is the first to show that BTX can be successfully used with CSB for treating CRION-induced ocular pain.
Case Presentation
A 34-year-old woman diagnosed with CRION 3 years earlier came to the clinic with biocular pain due to ON. She had been treated at another hospital for ON before but had persistent biocular pain for the past 2 years. Her numeric rating scale (NRS) pain score was 8 – 10/10, and the pain was worse with eye movement and wind exposure. After a neurological examination, it was found that she was completely blind in the right eye, and the left eye was gradually losing sight. NMO-immunoglobulin G was seronegative. Sella magnetic resonance images showed contrast enhancement of the bilateral inflamed optic nerves. Medical records from the previous hospital showed she responded to immunosuppressive treatment but relapsed when the dose was reduced. She continued immunosuppression treatment under neurology consultation, but proper pain treatment was never given.
Initially, CSB with a local anesthetic was done several times under ultrasound guidance, but the analgesic effect didn’t last more than 1 day. Pulsed radiofrequency of the CST (42°C, 120 s, four cycles) was done on both sides at regular intervals but had no effect.
Then, CSB with BTX was performed under ultrasound guidance. First, a 13 to 6 MHz linear probe was placed in the neck, and the CST location was confirmed at the surface of the longus capitis at the level of the fourth cervical vertebra. The needle was placed on the longus capitis, and a mixture of BTX and bupivacaine was injected. Since her right eye had no vision, the left side was treated first. 50 units of BTX (Botox®; Allergan Inc., Irvine, CA, USA) were mixed with 5 mL of 0.5% bupivacaine and injected into the left CST. About 3 days later, the NRS pain score decreased from 10 to 5, and the effect lasted 4 weeks. She could open her left eye, which was impossible before due to severe pain. But one week after the injection, she complained of dysphagia and neck weakness, which lasted 4 weeks and resolved without targeted treatment.
In the second trial, 25 units of BTX mixed with 5 mL of 0.2% bupivacaine were injected around the left CST. Similar to the first trial, she had dysphagia and neck weakness. In the third trial, 7.5 units of BTX mixed with 0.3 mL of 0.2% bupivacaine were injected into the left CST. No analgesia or side effects were seen. In the fourth trial, 10 units of BTX mixed with 1 mL of 0.2% bupivacaine were injected into the left CST. The analgesia lasted about 4 weeks without side effects. Finally, she was successfully treated on both sides.
Discussion
This case report shows that injecting BTX around the CST is effective for managing ocular pain from CRION-induced ON. CSB is commonly used to alleviate head and neck neuropathic pain. Since a single sympathetic nerve block’s effect can be short, pulsed radiofrequency of the CST is an alternative. But it didn’t work for this patient, maybe because it’s hard to evoke sensory perception via sensory stimulation during pulsed radiofrequency in the CST. So, injecting BTX was the next step. Although no report has been published on its use for ocular pain, a study using rabbits found that CSB with BTX caused miosis (lasting 1 month) without pathological changes.
Since few studies have looked at BTX injections during CSB, the optimal dose and volume of BTX are unknown, and side effects are rarely reported. In cervical dystonia studies, injecting BTX into the cervical muscle is preferred. When treating cervical dystonia with onabotulinumtoxinA, the incidence of dysphagia is 7.1%. When BTX is given into the sternocleidomastoid muscle, dysphagia can result from pharyngeal muscle weakness due to regional spread. Chang et al hypothesized that dysphagia after BTX injection into the sternocleidomastoid is from hyperactivation of the suprahyoid and infrahyoid muscles to compensate for a weakened sternocleidomastoid. In cervical dystonia reports, the total dose of onabotulinumtoxinA varies from 60 units to 374 units. In this case, the doses were smaller than for cervical dystonia. The dysphagia after CSB, even at a lower dose of 50 units, might be because dysphagia is greater when administered over the fascia between muscles than intramuscularly. To confirm the safest and most effective BTX dose and volume, a larger clinical study is needed.
In conclusion, this case provides valuable insights into using BTX with CSB for CRION-induced ocular pain. It opens up new possibilities for pain management in this complex condition, but more research is required to optimize the treatment.
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doi.org/10.1097/CM9.0000000000001590
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