The diagnosis of blepharospasm is not always easy, in particular in case of pretarsal blepharospasm, also called Apraxia of eyelid opening, mistaken quite often for ocular myasthenia.
1- what is ocular myasthenia?
Myasthenia is an autoimmune disease, responsible of muscle weakness, affecting the all body and when localized to the muscles around the eyes, called ocular myasthenia.
Ocular myasthenia can present with isolated droopy eyelids (medically called ptosis), due to a weakness of the levator muscles of the eyelids, the Levator Palpebrae, but is often associated with double vision, due to weakness of the oculomotor muscles. The weakness is worst at the end of the day, due to the fatigue of the myasthenic muscles.
The diagnosis of ocular myasthenia is based on clinical findings, the presence of antibodies in the serum (30 to 60% cases) and the abnormal response of the muscles on repetitive electrical stimulation. Clinically the doctor can look for the “peek sign” by asking the patient to perform a sustained gentle eyelid closure; the fatigue of the orbicularis oculi will be responsible of a slight opening of the eye, as the patient peeking.! ( J. Glaser).
2- why so many patients with Blepharospasm are misdiagnosed with ocular myasthenia?
-Blepharospasm patients can have a misleading presentation of ptosis, with intermittent droopy eyelids, due to the spasms of the pretarsal portion of the orbicularis oculi muscles (also described as pretarsal BSP) pulling down the eyelid like the string of a roller blind down to the window.
-The words that patients used to describe their symptoms such as “my eyes are tired”, “my eyelids feel heavy”, “I feel more comfortable eyes closed” can indicate wrongly a muscle weakness of the eyelids, and reflect in fact the loss fight of the patients against the dystonic spasms closing their eyes.
– the variability of the symptoms through the day ; in myasthenia the patient is worst at the end of the day; in BSP the patient is worst walking outdoors, driving, watching TV, looking up and with any bright light and dazzy winter light.
– A levator palpebre detachement can occurs on some patients after years of spasms, and pulling on the muscle insertion
3-the art of lid watching
The famous neuro-ophtalmologist, J Glaser talked about “ Lid watching, a lost art!” Joel Glaser in Handbook of neuro-ophthalmology, 1999
-Lid watching is optimal when patients are keeping silent; BSP patients have an increased rate of blinking when being quiet and vice versa a low blinking rate when speaking. It’s the opposite of what observed in normal subjects. That may explain why patients find easier to keep her eyes opened when speaking and choose to sing when driving.
-In the case of pretarsal BSP careful lid watching along the eyelashes, looking for a pulling down spasms of the eyelids is a good indicator of pretarsal spasms.
– In addition, the lid closing spasms may be associated with Bell’s phenomenon with elevation of the eyeball, so it’s important to look not only at the eyelid but also the eyeball
– In case of levator palpebre detachment, the forceful opening of the eyes on command will be limited;
– Also the patients sometimes can’t reopen their eyes, after a spontaneous blink or after a closing spasm. It can be for a fraction of second or for up to few minutes; the patient will flicker his eyelashes, or his eyelids to kick them opened. Sometimes it will be a forceful pulling of the eyelids with his fingers, stretching the skin around the eyes, even sometimes resulting in bruising.
All these signs found on careful lid watching are good indicators of eyelids spasms, and not eyelid droopiness. They also direct the hands of the injector to the maximum spasms to achieve optimal results.
In the movement disorders field, most of the diagnosis are made by watching the movement; it’s particular true for eyelid dystonia and vocal cords dystonia where immobility does not always equal paralysis but also permanent tension due to the dystonia; one day I will ask my ENT colleagues to tell us about the art of vocal cords watching!!!