The spectrum of Möbius syndrome: an electrophysiological study

Abstract

We studied the nature and extent of facial muscle innervation and the involvement of the motor and sensory long tracts in Möbius syndrome, in order to shed light on the pathophysiological mechanism of the syndrome. Standardized blink reflexes, direct responses of the facial nerves to the orbicularis oculi muscles and concentric needle electrode electromyography in orbicularis oculi and/or oris muscles were measured in 11 patients with Möbius syndrome, of whom six participated in MRI studies, all showing absent facial nerves. We performed motor- and somatosensory-evoked potentials in seven Möbius patients. We demonstrated three distinct patterns of abnormalities suggesting different sites of the primary lesion in different patients. (i) Presence of normal blink reflexes and facial compound motor action potentials, normal habituation tests, a reduced recruitment in the facial muscles and an aberrant 'blink reflex-like' response of the orbicularis oculi muscle upon stimulation of the facial nerve region, which suggests a supranuclear origin of the defect. (ii) Absent blink reflexes, absent direct responses of the facial nerves and absent motor activity on needle electromyography, indicating a defect at the facial nuclear level. However, the nuclear defect might mask an additional supranuclear defect, which cannot, therefore, be excluded in these patients. (iii) A disperse pattern of facial compound action potentials combined with long latencies that were recorded with concentric needle electrodes, indicating involvement of motor axons in the facial nerve, possibly secondary to nuclear involvement. An additional supranuclear defect cannot be excluded in these cases. All evoked potentials studied were normal. The electrophysiological findings of the facial muscles show a spectrum of disturbances varying in degree of severity and diverse in the extent of structures involved, in 11 Möbius patients. At one end of the spectrum are patients with completely immobile faces in whom electrophysiological testing shows no signs of involvement of the facial nuclei, nerves or muscles, suggestive of a dysfunction at the supranuclear level. At the other extreme of the spectrum are patients with complete absence of responses upon facial nerve stimulation and absence of motor unit activity. This is at least indicative of a defect at the facial nuclear level. While a supranuclear defect is compatible with the concept that Möbius syndrome is a developmental disorder of the lower brainstem, intact facial nuclei as part of the syndrome has not been suggested before. The findings corroborate the concept of the Möbius syndrome being a complex regional developmental disorder of the brainstem.

Duane Retraksiyonu Olan Mobius Sendromu: Abdusens Sinir Yokluğu ve Fasyal Sinir Hipoplazisi

“…Their findings agreed with Verzijl et al's that Mobius syndrome is a complex syndrome of rhombencephalic maldevelopment involving predominantly motor nuclei and axons. 15 However, Dumars et al 16 reported extraneuronal findings which included hypoplasia of the posterior bony orbit, displaced rectus muscle paths, and abnormal insertions of the superior and inferior oblique muscles, which show that it is not only a brain stem dysplasia. Thereby, it remains unknown whether the primary defect is actually maldevelopment of brainstem nuclei, nerves, or their associated muscles, and whether the process is dysplastic or degenerative.…”

Atypical facet of Möbius syndrome: Association with facioscapulohumeral muscular dystrophy

“…When ocular motility is limited in Möbius presentations this typically involves horizontal eye movements. 9,12 Möbius syndrome in rare instances has been associated with complete ophthalmoplegia, but in one case this was presumed to be due to a supranuclear lesion. 9 Furthermore, our patient exhibited generalized facial diplegia, which differs from the pattern of relative sparing of lower facial muscles characteristic of Mö-bius syndrome.…”

“…9 Furthermore, our patient exhibited generalized facial diplegia, which differs from the pattern of relative sparing of lower facial muscles characteristic of Mö-bius syndrome. 12 Although cases of congenital facial diplegia with early onset shoulder-girdle weakness have been reported in conjunction with the FSHD phenotype and 4q35 deletion, 2,5 it is generally accepted that FSHD spares the extraocular muscles. 10 Unlike some patients with FSHD, there was no evidence of sensorineural deafness or Coat's syndrome (bilateral retinal exudative telangiectasia).…”

“…12 Since the 1960s it has become clear that Möbius syndrome might be secondary to progressive myopathic diseases, including myotonic dystrophy. The first description of congenital facial diplegia associated with a progressive myopathy resembling facioscapulohumeral dystrophy (FSHD) was in 1971.…”

Facial animation in patients with Moebius and Moebius-like syndromes

“…Moebius syndrome/sequence is a rare congenital disorder of varying severity characterised by bilateral or unilateral paralysis of the facial and abducens nerves 1,3,4,7,14,17,19,20 . Its aetiology is unknown, but environmental and genetic factors have been implicated.…”