Nour Houbby, Osama Munajjed
Introduction
Benign essential blepharospasm is a focal dystonia relating to the involuntary contraction of the orbicularis oculi, procerus and corrugator muscles (1). The exact pathophysiology underlying benign essential blepharospasm remains unknown, although both genetic and environmental components are thought to underly the development of benign essential blepharospasm (2). This precipitates an abnormal and repetitive bilateral eyelid closure which results in functional blindness and significantly impacts patient morbidity and quality of life (3). Benign essential blepharospasm is additionally associated with apraxia of eyelid opening, which compounds the resultant disability experienced by these patients (4). It has an estimated prevalence of 4 per 100,000 people, more commonly affecting middle aged women in comparison to their male counterparts (5). Clinical presentation is of involuntary eye spasms which are bilateral and chronic which may also occur with other dystonic movements. Several treatment options exist for benign essential blepharospasm including botulinum toxin, systemic oral medications and surgical management options (6).
Presenting symptoms
Benign essential blepharospasm predominantly affects people of middle age (between the ages of 50-70) and more commonly affects women (7). A detailed clinical history is essential to determine the symptoms and signs the patient is experiencing. Common precipitant factors are stressful life events which occur prior to symptom development (8). The clinical manifestations of benign essential blepharospasm are characterized by a bilateral, synchronous spasm of the eye muscles which causes repetitive blinking and eye closure which may eventually lead to functional blindness. These symptoms are often highly variable and there is variance depending on individual patients, ranging from a mild increasing blinking rate to more severe symptoms of total functional blindness. Some patients may additionally suffer from apraxia of eyelid opening which is the inability to reopen eyes which occurs from the spasm of the pretarsal orbicularis oculi muscle (9).
In addition to the ocular manifestations discussed, several other symptoms may occur including sensory symptoms and psychiatric symptoms. Sensory symptoms such as dry eyes and irritation have also been reported by patients. Anxiety and depressive symptoms are often seen in benign essential blepharospasm (10). These psychiatric manifestations may be a trigger for the development of the disease, or they may occur due to the significant psychosocial burden it incurs.
Several rating scales have been developed in order to assess the severity of the disease (11). The Jankovic Rating Scale is most commonly used in the assessment and monitoring of patients which is made up of two subscales- severity and frequency of symptoms (12). During the assessment of patients with benign essential blepharospasm, several differential diagnoses must be considered. These include hemifacial spasm, apraxia of eyelid opening (which can often occur alongside benign essential blepharospasm), facial tics, psychogenic facial spasm, facial myokymia and tardive dyskinesia (13).
Management
The main treatment modalities which currently exist for benign essential blepharospasm include chemodenervation with botulinum toxin, oral medications and surgery in refractory cases (14).
Certain alternative treatments such as acupuncture have also been used by certain patients.
Botulinum toxin injections
Botulinum toxin injection is considered to be one of the mainstays of treatment for benign essential blepharospasm as it achieves reduced muscle contraction through inhibiting the release of acetylcholine at the neuromuscular junction (15). The treatment involves injection of botulinum toxin into several injection sites such as the orbicularis oculi, procerus and corrugator muscles. Clinical response is commonly observed within 48 hours and is dose-dependent, with effects lasting on average up to three months (16). Several complications are associated with botulinum toxin injections including diplopia, photophobia, blurred vision, of which ptosis is the most commonly reported side effect which occurs due to the spread of the botulinum toxin into the levator palpebrae superioris muscle (17). Botulinum toxin remains the most common treatment for benign essential blepharospasm, however, it must be noted that effects of treatment are transient and therefore must be repeated resulting in an increased disease burden and an increased complications rate with repeated use.
Medications
Dystonic disease phenomena have historically been treated with oral systemic medications, however they are not considered the mainstay of treatment given the variable response that is achieved in patients (18). Medications have been used as an adjunct to botulinum toxin therapy, or in cases of refractory disease prior to surgical intervention or in cases where surgical intervention may not be a possibility. Several oral medications have been used, with variable efficacy and side effect profile however there is currently no single medication which proves to be most effective at symptom eradication (19). Examples of medication classes which have been used in the treatment of benign essential blepharospasm include dopaminergics, anticholinergics, GABA agonists amongst others.
Surgical interventions
Surgical management may be considered in patients who have symptoms which are refractory to medical management (20). Surgical interventions include myectomy, neurectomy amongst others. For example, surgical myectomy involves the resection of the protractor muscles and can achieve good results. However, it must be noted that these procedures are not without postoperative complications such as infection, periorbital swelling, hemorrhage, facial anaesthesia, and corneal irritation (6).
Conclusion
Benign essential blepharospasm is a condition which can cause significant functional disability for patients. A multidisciplinary approach to care is crucial with tailored treatment on a case-by-case basis.
References
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