Assessment of infantile dystonia

Abnormal movement disorders are classified as parkinsonism, dystonia, tremor, chorea, myoclonus, tics, stereotypies, and complex movement disorder. Dystonia is described as contraction of both agonist and antagonist muscles simultaneously, causing twisting and repetitive movements or abnormal postures. [1] Fahn S, Bressman SB, Marsden CD. Classification of dystonia. Adv Neurol. 1998;78:1-10. http://www.ncbi.nlm.nih.gov/pubmed/9750897?tool=bestpractice.com The earlier the age of onset, the more generalised and severe the condition tends to be.

Dystonic movements

Dystonic movements are patterned and sustained. They repeatedly involve the same muscle groups. The urge to perform the dystonic movements is absent, and there is no relief after the dystonic movements are executed. Dystonia usually gets worse with fatigue and emotional stress and it gets better with sleep and relaxation. [2] Geyer HL, Bressman SB. The diagnosis of dystonia. Lancet Neurol. 2006 Sep;5(9):780-90. http://www.ncbi.nlm.nih.gov/pubmed/16914406?tool=bestpractice.com [3] Obese JA. General concepts. In: Fernández-Alvarez E, Aicardi J, eds. Movement disorders in children. London: Mac Keith Press; 2001:1-23. Photographs and video footage of affected infants are helpful in delineating the dystonic movements. Periodic follow-up is often a prerequisite to making an accurate diagnosis.

Types of infantile dystonia

In the classification of dystonias, the term infantile refers to onset from birth to 2 years of age. [4] Albanese A, Bhatia K, Bressman SB, et al. Phenomenology and classification of dystonia: a consensus update. Mov Disord. 2013 Jun 15;28(7):863-73. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729880/ http://www.ncbi.nlm.nih.gov/pubmed/23649720?tool=bestpractice.com Dystonias are described according to two complementary axes: [4] Albanese A, Bhatia K, Bressman SB, et al. Phenomenology and classification of dystonia: a consensus update. Mov Disord. 2013 Jun 15;28(7):863-73. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729880/ http://www.ncbi.nlm.nih.gov/pubmed/23649720?tool=bestpractice.com

• Clinical characteristics (axis 1), which include age at onset, body distribution, temporal pattern, and associated features

• Atiology (axis 2), which includes nervous system pathology and inheritance.

Information from the history and physical examination allows an initial classification and differential diagnosis to be made. The presence and absence of motor features and other signs and symptoms can narrow the differential diagnosis by indicating a particular dystonia syndrome and by directing the diagnostic evaluation towards groups of disorders associated with different clinical patterns, such as:

• Isolated dystonia (dystonia alone or dystonia with tremor)

• Combined dystonia (dystonia with other motor features)

• Complex dystonia (dystonia with other symptoms).

The clinical evaluation may also indicate whether the condition is neurodegenerative or suggest an acquired or inherited aetiology.

Further investigations may be required including neuroimaging, evaluation for associated neurodevelopmental or systemic abnormalities, therapeutic trial of levodopa, or biochemical (including diagnostic lumbar puncture) and genetic tests.

Several pseudo-dystonias need to be considered in the differential diagnosis; these conditions involve dystonia-mimicking abnormal movements, but their aetiologies differ from those of dystonias.

The rapid identification of several conditions is important to prevent irreversible injury or death:

• Drug-induced acquired dystonia

• Pseudo-dystonia due to cervical instability

• Status dystonicus

• Multiple neurometabolic disorders, such as glutaric aciduria type I

• Acute bilirubin encephalopathy.

Many metabolic disorders present in infancy, and are high on the list of likely differential diagnoses in the first year of life. [4] Albanese A, Bhatia K, Bressman SB, et al. Phenomenology and classification of dystonia: a consensus update. Mov Disord. 2013 Jun 15;28(7):863-73. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729880/ http://www.ncbi.nlm.nih.gov/pubmed/23649720?tool=bestpractice.com [5] Sanger TD. Pathophysiology of pediatric movement disorders. J Child Neurol. 2003 Sep;18 Suppl 1:S9-24. http://www.ncbi.nlm.nih.gov/pubmed/13677568?tool=bestpractice.com

Dopa-responsive dystonia (Segawa syndrome, dystonia-parkinsonism with diurnal fluctuation) needs to be considered in any infant or child with unknown diagnosis and normal MRI. It is usually misdiagnosed as spastic diplegic or quadriplegic cerebral palsy, intractable epilepsy, or hereditary spastic paraplegia. [6] Kamal N, Bhat DP, Carrick E. Dopa-responsive dystonia (Segawa syndrome). Indian Pediatr. 2006 Jul;43(7):635-8. http://www.indianpediatrics.net/july2006/635.pdf http://www.ncbi.nlm.nih.gov/pubmed/16891685?tool=bestpractice.com [7] Jan MM. Misdiagnosis in children with dopa-responsive dystonia. Pediatr Neurol. 2004 Oct;31(4):298-303. http://www.ncbi.nlm.nih.gov/pubmed/15464646?tool=bestpractice.com