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Arnold-Chiari malformation type I (ACM I) is a developmental anomaly of the rhombencephalon characterised by displacement of the cerebellar tonsils into the foramen magnum and elongation of the medulla. It usually presents in adult life with head motion induced oscillopsia, ataxia, headaches, cervical pain, or Valsalva induced dizziness.1
Various ocular motor abnormalities have been reported in patients with ACM I. Among these, downbeat nystagmus and periodic alternating nystagmus are the most common. Other often encountered ocular signs, such as gaze evoked nystagmus, rebound nystagmus, and impaired smooth pursuit, reflect cerebellar involvement.2 3
Vertigo of vestibular origin, being peripheral or central, is usually accompanied by nystagmus and nausea, or vomiting, and is often influenced by head position.3 4 The entity of central positioning vomiting without, or little, vertigo and nystagmus (posturally evoked vomiting (PEV)) was first reported by Drachmanet al and later recognised by Brandt and Baloh and Halmagyi.3-5
Posturally evoked vomiting is generally poorly known as a warning symptom of a posterior fossa lesion and is often misinterpreted.5 Whereas it has been documented in patients with posterior fossa tumours, it has not been reported in patients with developmental abnormalities. We report on a patient with ACM I where PEV was the most prominent presenting symptom.
This 57 year old woman was seen in our vertigo clinic because of gait unsteadiness and postural vomiting. Her history included an aortic valve replacement for aortic insufficiency, nephrolithiasis, and peptic disease. She was treated with warfarin.
For years, she had dizziness and severe nausea while looking up. During the past months severe nausea and vomiting appeared when she tilted her head to either side and down. Lately, she had become unsteady. She also complained about left high pitched tinnitus and intermittent pain in the left shoulder.
On examination her eyes were properly aligned with a full range of movements. No primary or gaze evoked nystagmus was seen, with and without Frenzel's glasses. The saccadic eye performance was normal, but the smooth pursuit in both the horizontal and the vertical plane was saccadic. The vestibulo-ocular reflex, examined by a doll's eyes movement, head thrust test, and dynamic visual acuity test, was normal. Mild dysmetria on finger-nose testing and finger-finger testing was found bilaterally. The deep tendon reflexes were brisk in the upper and normal in the lower limbs. The plantar toe responses were flexor. Sensation was normal. The gait was atactic and the Romberg test negative.
On testing the eyes in the Dix-Hallpike position to either ear, as well as in the head down position, the patient reported severe nausea, and became pale and perspired. However, no nystagmus was seen either by direct observation, or with Frenzel's glasses.
The symptoms persisted with repetition of the positioning.
An electronystagmogram (ENG) documented saccadic eye tracking in the horizontal plane. The optokinetic nystagmus was asymmetric with little increment after increased speed velocity of the target. When supine and with her head turned to the left, nystagmus of 7°/s, beating to the left, was recorded. No nystagmus was recorded on Hallpike testing.The caloric test was within normal limits.
A behavioural audiogram showed mild bilateral sensorineural hearing loss in the frequencies of 2000 Hz-8000 Hz with normal speech discrimination, interpreted as presbyacusis. The brain stem auditory evoked potentials were normal.
Brain T1 and T2 weighted MRI with gadolinium enhancement disclosed low lying cerebellar tonsils with elongation of the medulla and pons, compatible with ACM I. A brain stem or cervical syrinx was not demostrable (fig 1).
In view of the progressive symptomatology, posterior fossa decompression was considered, but postponed because of the cardiac situation of the patient. Clonazepam was offered to the patient for alleviation of the posturally evoked symptoms, but was refused because of possible sedation.
Central paroxysmal positioning vertigo occurs transiently on changing the head position, as opposed to central positional nystagmus, which persists as long as the head position is sustained.3 4Central paroxysmal positioning vertigo can be differentiated from benign paroxysmal positioning vertigo by its shorter latency, longer duration of the attack, and a direction changing nystagmus which is not attributable to stimulation of a single canal.3 4 It usually indicates a lesion around the fourth ventricle, dorsal vermis, or diffuse cerebellar pathology.3 Central positional nystagmus is often bilateral, of low constant frequency, and occurs in association with lower brain stem or vestibulocerebellar lesions.3
In 1977 Drachman et al described the entity of PEV.5 In their two patients (one with a metastasis and the other with a glioblastoma of the cerebellar vermis) PEV was a prominent clinical sign, whereas vertigo and nystagmus diminished with the progression of the pathological process. Positional vomiting became so severe that the patients had to hold their head in a forced position to prevent vomiting. The symptoms cleared after treatment with vestibular suppressants. Drachman et alexplained the condition of PEV by dissociation of the vomiting centres from oculomotor and receptive pathways of the complex vestibular syndrome by a brain stem infiltrating lesion.
Arbusow et al described a patient with amiodarone induced positional vomiting with mild vertigo, downbeat nystagmus, and limb ataxia, responsive to benzodiazepines. According to their concept, which is in keeping with that of Drachmanet al, amiodarone disinhibits selectively the connections between the dorsal cerebellar vermis and the vomiting centres in the postremal area and the lateral reticular formation, sparing relatively the vermis-ocular motor circuity.6
Severe positioning nausea and vomiting with inconsistent dizziness and without nystagmus, was present in this patient with ACM I. Initially, nausea occurred only on head extension, but later on all head movements but anteflexion. An ENG showed only low speed positional—that is, sustained nystagmus in one head direction. On Hallpike positioning testing nystagmus was not recorded. Other ocular motor findings (saccadic pursuit and abnormal optokinetic nystagmus ) were compatible with a cerebellar lesion.3 4
In ACM, a normal vestibular input after changes in head position might be misprocessed by transient brain stem compression, leading to dissociation of the vomiting centres from other parts of the vestibular reflex. The relatively mild signs of positional vomiting in our patient might be due to the benign nature of the underlying disease, as opposed to the invasiveness of tumours or acute neurotoxicity, leading to severe PEV.5 6
This patient with ACM seems to be unique in the literature, as PEV has not been reported in this clinical setting.
Further neurophysiological studies are needed to elucidate the pathogenesis of PEV.