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Neurology India, Vol. 58, No. 1, January-February, 2010, pp. 135-136 Letter To Editor Paroxysmal exercise-induced dystonia with optic atrophy: A-30-year follow-up A. J. Larner, A. Jacob1 Department of Neurology, Walton Centre for Neurology and Neurosurgery, Liverpool, L9 7LJ, United Kingdom, Correspondence Address: A. J. Larner, Department of Neurology, Walton Centre for Neurology and Neurosurgery, Liverpool, L9 7LJ, UK, a.larner@thewaltoncentre.nhs.uk Date of Acceptance: 13-Aug-2009
Code Number: ni10031 DOI: 10.4103/0028-3886.60399 Sir, Sporadic paroxysmal exercise-induced dystonia (PEID) is a rare condition. A recent review identified only 15 cases in the world literature, [1] more than half from one British series. [2] A familial syndrome of paroxysmal dystonia induced by exercise such as walking was first described in 1984, [3] and subsequent reports broadened the phenotype to include migraine [4] and epilepsy. [5] Genetic studies have shown no linkage of familial PEID to loci linked to paroxysmal nonkinesigenic dystonia or familial hemiplegic migraine. [4] We present a further patient with sporadic PEID with additional optic atrophy, pendular nystagmus, and migraine with aura, who has been followed-up and investigated over a period of more than 30 years. From the age of 18 months, a Caucasian female, born by normal full-term delivery, product of nonconsanguineous parents, developed episodic attacks characterized by painless flaccid weakness of all limbs coming on after exercise, such as walking for half a mile, with bending truncal movements to the left and dystonic movements of the hands, and sometimes associated with dysarthria. Attacks persisted for hours, improved after sleep, were not influenced by ambient temperature, and were not associated with any impairment of consciousness. From the age of five years, the child′s visual acuity deteriorated, with development of bilateral optic atrophy and pendular nystagmus. As a teenager, she developed typical migraine with aura, but the attacks of limb weakness became less frequent and severe. Now in her mid thirties, she has residual feelings of left-sided weakness and reduced exercise tolerance, but has no further episodic attacks, and has developed no neurological signs aside from the longstanding optic atrophy and pendular nystagmus. She has had two uneventful pregnancies. Neither myoclonus nor myokymia has ever been observed, and there is no deafness. Intelligence has been preserved throughout. There is no family history of similar disorder. Investigations during childhood attacks showed repeatedly normal serum potassium, creatine kinase and lactate. Thyroid function tests were normal. Electromyography (EMG) was normal both during and immediately after attacks. A tensilon test was negative. Two muscle biopsies, performed at the age of four and 16 years, were morphologically normal (no ragged red fibres), and biochemical studies for mitochondrial disorder were also negative. Investigation of her visual problems included an electroretinogram (normal) and flash visual evoked responses which showed no cortical responses. Magnetic resonance imaging (MRI) of the whole neuraxis in her twenties was normal, as was a standard EEG recording, and repeat EMG (aged 28). Neurogenetic testing for mitochondrial point mutations associated with MELAS, MERFF, and NARP (3243, 8344, 8993) and with Leber′s hereditary optic neuropathy (3460, 11778, 14484) were all negative, as was testing for the Friedreich′s ataxia triplet expansion. She has declined a further muscle biopsy. Empirical trials of acetazolamide as a child and in her twenties, and of levodopa in her late twenties and early thirties were without therapeutic benefit. Alcohol has had no affect on the attacks. This patient presented as a child with attacks typical of paroxysmal episodic dystonia following exercise, with no family history of similar problems, and hence, a diagnosis of sporadic PEID was made. Whether this movement disorder and the optic atrophy which subsequently developed represent chance concurrence or related comorbid conditions is not entirely clear, but we favor the latter explanation, which would mean that this case broadens the phenotype of sporadic PEID. Likewise, the migraine with aura developing in teenage could be chance concurrence; although this has been described in familial PEID [4] but not in sporadic PEID to the best of our knowledge. The phenotype clearly differed from a previously reported familial progressive dystonia with optic atrophy syndrome, [6] since dystonia was not progressive and brain imaging was normal. An aetiological diagnosis has not been established in this patient, as is the case in previously reported cases. [1],[2] A mitochondrial disorder was initially suspected on clinical grounds, but no investigational evidence to support this diagnosis has ever been found. However, normal muscle biopsy and negative neurogenetic testing in blood may occur in mitochondrial disorders (genetic testing may be positive in perhaps only approximately 15% of the mitochondrial disorders), and for confirmation actual measurement of mitochondrial enzyme complex from muscle tissue is required. This was not performed on our patient′s original biopsies and further investigation has been declined. Familial cases of "mitochondrial-like" early-onset dystonia and optic atrophy with normal complete mitochondrial DNA sequence have been reported. [7] The possibility that this patient has channelopathy, as found in some other paroxysmal movement disorders, has also been considered, but this has yet to be defined. References
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