Abstract
Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.
Highlights
Inborn errors of metabolism (IEMs) are defined as any condition that leads to a disturbance of a metabolic pathway, irrespective of whether it is associated with abnormalities in biochemical laboratory tests
The 51% of IEMs of this review presents 2 or more Movement Disorders (MD)
Some tests of the second-tier should be considered at the beginning of the diagnostic process if the suspicion of a particular disease is very high. This list of biochemical tests is broader for patients with ataxia, the most frequent MD in patients with IEMs and the one with the most possible etiologies whereas the list become more restricted for patients with myoclonus and hypokinetic-rigid syndrome
Summary
Inborn errors of metabolism (IEMs) are defined as any condition that leads to a disturbance of a metabolic pathway, irrespective of whether it is associated with abnormalities in biochemical laboratory tests. IEMs encompass a large group of single gene disorders that can affect all organs and lead to a variety of symptoms [2]. MD manifest in IEMs that cause diffuse CNS or selective basal ganglia involvement. As it is known, the basal ganglia participate in the control of voluntary movement and on the other hand this brain area is especially vulnerable to certain IEMs as metal storage defects, energy metabolism and lysosomal storages disorders [4, 5]. A central problem is the large number and variety of IEMs with MD and the poor recognition of these disorders that make it challenging for the pediatric neurologist to decide on the initial evaluation with the consequent delay in diagnosis and timely treatment. This work facilitates an update information with new IEMs that present MD, suggests red flags and diagnostics clues for suspecting IEMs, proposes the minimum biochemical studies as stated in each MD and the differential diagnoses according to the neuroradiological findings and provides evidence on symptomatic or disease specifictreatment through a six-step algorithm
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