Compared to systemic treatments, local injections treated symptoms faster, reduced side effects, and increased remission rate.
The study, “Local use of dexamethasone in the treatment of ocular myasthenia gravis,” was published in the journal BMC Ophthalmology.
Myasthenia gravis (MG) is caused by the body’s immune system attacking proteins at the site where nerve cells connect and transmit signals to muscles, resulting in muscle weakness.
In ocular MG, which accounts for about 15% of all MG cases, the symptoms are limited to muscles that control the eyes and eyelids. Ocular MG typically is treated with systemic therapies such as acetylcholinesterase inhibitors and corticosteroids that travel through the bloodstream. Although systemic medications are effective at treating ocular MG, they can cause serious side effects that affect quality of life.
Local medication, administered at the treatment site, has been used as an effective treatment for other eye disorders, including topical corticosteroids to treat uveitis (inflammation) associated with juvenile idiopathic arthritis, and local hormone injections to treat thyroid-related ophthalmopathy. In addition to their efficacy, local treatments typically have fewer side effects than systemic therapies.
Here, researchers conducted a clinical trial (ChiCTR2000038863) to determine if local injections of dexamethasone could be effective and safer than systemic treatment for people with ocular MG.
The 14 patients in the study — mean age 38.7, range 8 to 92 — were diagnosed with ocular MG from August 2016 to May 2019 at Wuhan Aier Eye Hospital in China. All patients had ptosis (drooping of the eyelid), strabismus, and double vision. Only three patients had normal eye movement, 12 had thymus enlargement, and six had antibodies against the acetylcholine receptor (the chief cause of MG).
Study participants received four to six once-weekly local injections of dexamethasone in the extraocular muscles that control eye movement, or the peribulbar region around the eye socket, based on their symptoms. They received either extraocular muscle injections of 0.5% dexamethasone and 2% lidocaine, or peribulbar injection of 0.5% dexamethasone. Symptoms were monitored monthly for six months after treatment.
All patients showed elimination of diplopia after four injections. Nine patients with limited eye movement alterations experienced resolution of ptosis. Yet, three participants required extra injections to restore muscle strength. The average time to eliminate symptoms was up to one week for ptosis, close to two weeks for diplopia, and around 4.5 weeks for eye movement.
Local dexamethasone injections in the present trial induced a faster recovery onset than oral steroids in prior studies, which normally take two to four weeks to ease symptoms and six to eight weeks to eliminate them. Notably, recovery from extraocular paralysis was the most difficult, and was related to the degree of muscle paralysis.
Two elderly patients did not experience complete elimination of their symptoms after two injections. A 92-year-old woman did not respond to treatment and a 73-year-old woman experienced complete elimination of diplopia, but only a slight reduction of ptosis.
The researchers tracked disease remission in all patients. A total of 12 patients (85.7%) achieved remission, including 11 who achieved treatment-independent remission and one who improved initially, but relapsed after recovery. Another patient was in therapy-dependent remission by the end of the study.
The overall remission rate in this study is significantly higher than that observed in previous studies of systemic ocular MG treatments such as oral prednisone, the team found. Significantly, none of the 14 participants experienced local or systemic side effects, with the exception of eye redness caused by the injection.
According to the investigators, the study was limited by its small sample size and lack of clinical comparison to systemic medications.
“Further studies will be necessary to determine the optimal site to be used for injection, the optimal time interval between injections and the optimal course of treatment. The stability of the curative effect achieved, the recurrence rate, and the rate of conversion will need to [be] investigated on a larger scale and for a longer period of time,” the researchers wrote.
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