Eating dysfunction associated with oromandibular dystonia: clinical characteristics and treatment considerations

In oromandibular dystonia (OMD) spasms of the masticatory, facial, and lingual muscles result in repetitive and sometimes sustained jaw opening, closure, deviation, or any combination of these as well as abnormal tongue movements [1]. Although most cases are idiopathic, neuroleptic drugs can induce OMD [2, 3]. OMD is very frequently associated with orobuccolingual (OBL) dyskinesias like facial grimacing, lip pursing and biting, tongue protrusion, rotation and/or dyskinesias, platysma contractions and bruxism [4]. A diagnosis of OMD carries with it a significant impact on quality of life [5]. Its treatment relies mainly on botulinum toxin type A injections that have been proven beneficial for all its subtypes [4].

Due to the anatomical distribution of the muscles affected, OMD and co-existing OBL dyskinesias are associated with disturbed perioral, oral and lingual movements that may interfere with the appropriate performance of tasks such as chewing, swallowing or talking, complicated with social embarrassment [6] and sometimes eating disorders with weight loss [7]. We present here the clinical characteristics and treatment variables of a series of patients that developed an OMD-associated eating dysfunction.

We performed a study of consecutive OMD patients followed-up at the Movement Disorders Clinic of the Department of Neurology of University of Miami, Miller School of Medicine over a 10-year period. We identified 53 patients with primary and secondary OMD. We excluded patients who were lost to follow up after initial evaluation or had inconclusive charts (n = 21) (only patients with at least 3 evaluations were included). Five out of 32 (15.6%) OMD patients reported symptoms of dystonic eating dysfunction. All OMD patients seen in our practice are routinely asked a set of specific questions about weight loss or eating difficulties associated with OMD (have you experienced difficulties eating? Have you experienced difficulties swallowing? Have you lost weight after the onset of your disease?). All patients were examined and followed-up by the same physician (CS). Results of treatment were analyzed using a global impression scale (0 = no improvement; 1 = mild improvement; 2 = moderate improvement; 3 = marked improvement). The formulation and preparation of botulinum toxin type A (BTX-A) (BOTOX^®, Allergan Pharmaceuticals, Irvine, CA, USA) was performed according to standard methods [8]. All patients that received BTX-A were injected bilaterally under EMG guidance, using an Allergan^® EMG needle. We recorded the muscles injected and the dose each muscle received. The mean dose of BTX-A for each patient was determined by adding the units injected per visit divided by the number of visits was used in the calculation of the mean dose (in units) of BTX-A in each group. The initial visit was not included since a lower than optimal dose of botulinum toxin was used.

Various studies have shown that a range of swallowing difficulties accompany focal cranio-cervical dystonias such as spasmodic dysphonia and spasmodic torticollis before treatment initiation [12–14]. Cervical dystonic contractions leading to anatomical swallowing dysfunction has been proposed as a possible mechanism [15, 16]. This interpretation may account for the dysphagia encountered in at least some of our OMD patients. Other proposed, previously reported mechanisms include excess duration of muscle activity, frequent co-contraction, loss of rhythmicity during chewing, and abnormalities in the chewing to swallowing transition phase [6]. These abnormalities, similar in type to those encountered in other forms of focal dystonia, may be the expression of an abnormal motor control of basal ganglia over mastication-related movement pattern generators of the brainstem [6].

Dysphagia has been also reported as a complication of BTX-A therapy in OMD [8, 17, 18]. However, none of our patients experienced further difficulty swallowing after receiving BTX-A injections. In fact, improvement was reported in 2 of the four of our patients who received this treatment.

Our study has some inherent limitations commonly seen in retrospective series. Documentation of all clinical and treatment variables may not be complete. However, all study patients have been evaluated and followed by the same movement disorders specialist (CS). Hence the impact of confounding factors such as inconsistencies in the diagnosis, inaccurate history, inter-examiner differences, and under-documentation were reduced. Furthermore, there are no additional evaluations of masticatory function (i.e. masticatory muscle EMG, jaw movement recording) other than weight loss (which may be influenced by many factors) and patient descriptions.

In summary, eating dysfunction was reported in 15.6% of our OMD cases. Eating dysfunction was associated with significant weight loss in three of our patients. Interestingly, only patients with OBL dyskinesias experienced weight loss. Additional difficulties included pain during eating, social embarrassment and speech disturbance. A measure of benefit was reported in the majority of our patients with BTX-A injections and oral antidystonic medications, especially tetrabenazine. Eating dysfunction associated with OMD should be identified and adequately characterized at the time of history taking and should be part of outcome measurements of the anti-dystonic treatment. Special attention has to be paid to patients with OMD and OBL dyskinesias since in our cases they experienced significant weight loss.