Infranuclear Oculomotor Disorders

Superior Oblique Myokymia

Clinical Aspects

Superior oblique myokymia is characterized by paroxysmal monocular high-frequency oscillations [6, 82, 83]. These oscillations are mainly torsional in the primary gaze position and in abduction, but when the eyes are in adduction the oscillations have a vertical component [83]. The patients usually complain of oscillopsia during these paroxysmal attacks.

Etiology

The pathophysiology of this condition is not totally clear, but vascular compression of the 4th nerve [84, 85] may be responsible. The same mechanism is suspected in vestibular paroxysmia. Alternative causes may include spontaneous discharges in the 4th nerve nucleus or of the superior oblique muscle.

Treatment

Like trigeminal neuralgia (another putative neurovascular compression disorder), superior oblique myokymia frequently remits spontaneously for periods of a few months to years. If it does not, a number of drugs have been reported to be beneficial, including the anticonvulsants carbamazepine [82] and gabapentin [86, 87]. In chronic cases that did not improve with anticonvulsants, tenotomy of the superior oblique muscle has been performed, but usually it necessitates inferior oblique surgery as well. Surgical decompression of the 4th nerve has also been reported to help, but this treatment should be reserved for the most vexing cases, as it may result in superior oblique palsy [88, 89] and bears a risk of suboccipital craniotomy. Treatment should always be started with one of the anticonvulsants.

Benign Paroxysmal Positional Vertigo

Clinical Aspects

One of the most frequent types of vertigo as well as oculomotor syndromes is benign paroxysmal positional vertigo (BPPV) [11, 90]. BPPV occurs when particles in one of the semicircular canals move freely when the head is turned in the plane of the affected canal. Theoretically, all three canals can be affected, but in practice the posterior vertical canal (p-BPPV) is affected most often [11, 90]. The positioning of the head towards the affected canal plane induces a rotatory nystagmus that beats to the undermost ear with a crescendo-decrescendo

time course. Horizontal BPPV (h-BPPV) is characterized by a nonfatiguable bilateral horizontal beating nystagmus that occurs while the patient lies supine and turns his/her head to the side of the affected canal [11, 91].

h-BPPV was reported to occur in about 12% of a series of 300 patients [91]. BPPV of the anterior vertical canal probably occurs much more seldom than that of the posterior or horizontal canal. The associated nystagmus charac-

teristically has less of a torsional component than in p-BPPV [92].

Etiology

BPPV is caused by the displacement of calcium-rich particles from the utricle into one of the canals [11, 90]. These particles change the function of the canal, which normally only detects angular acceleration. If the head is positioned in the plane of the affected canal, the particles move within the semicircular canal according to the gravitational force, causing an endolymph flow that is followed by a displacement of the cupula of the canal. Predisposing conditions are older age, head trauma, labyrinthitis, Menière’s disease, migraine, or longer periods of immobilization.

A differential diagnosis of positional vertigo is migrainous vertigo; it may mimic BPPV. Several groups recently reported an association of migraine and vertigo. A study published this year classified 10 patients of 362 consecutive patients who had positional vertigo as well as migrainous. Diagnostic factors that distinguish the migrainous form from idiopathic positional vertigo are short duration of the attacks, frequent recurrences, early manifestation in life, other migrainous symptoms like photo-/phonophobia and headache during the vertigo episodes, and atypical nystagmus [93]. Central positional vertigo due to lesions of the vestibular cerebellum can mimic peripheral positional vertigo sometimes, but normally the nystagmus is less pronounced and does not show habituation [94].

Treatment

Treatment consists of so-called liberatory maneuvers. The rationale is to redirect the particles out of the affected canal. There are two repositioning treatments for p-BPPV: Epley’s and Semont’s maneuvers. Both require active movements by the patients; this may be difficult for older patients. Another possibly effective therapeutic procedure is the so-called prolonged forced position. It requires the patient to maintain a position in which the affected ear remains uppermost for several hours. This is thought to allow the floating particles to slip out of the canal into labyrinthine recesses, where they no longer have any impact on the cupula [95].

The question as to which liberatory maneuver is superior for benign positional paroxysmal vertigo of the posterior canal was recently addressed in