AIM: Hyperkinetic movement disorders (HMDs) can be assessed using 
impairment-based scales or functional classifications. The Burke-Fahn-Marsden 
Dystonia Rating Scale-movement (BFM-M) evaluates dystonia impairment, but may 
not reflect functional ability. The Gross Motor Function Classification System 
(GMFCS), Manual Ability Classification System (MACS), and Communication Function 
Classification System (CFCS) are widely used in the literature on cerebral palsy 
to classify functional ability, but not in childhood movement disorders. We 
explore the concordance of these three functional scales in a large sample of 
paediatric HMDs and the impact of dystonia severity on these scales.
METHOD: Children with HMDs (n=161; median age 10y 3mo, range 2y 6mo-21y) were 
assessed using the BFM-M, GMFCS, MACS, and CFCS from 2007 to 2013. This 
cross-sectional study contrasts the information provided by these scales.
RESULTS: All four scales were strongly associated (all Spearman's rank 
correlation coefficient rs >0.72, p<0.001), with worse dystonia severity 
implying worse function. Secondary dystonias had worse dystonia and less 
function than primary dystonias (p<0.001). A longer proportion of life lived 
with dystonia is associated with more severe dystonia (rs =0.42, p<0.001).
INTERPRETATION: The BFM-M is strongly linked with the GMFCS, MACS, and CFCS, 
irrespective of aetiology. Each scale offers interrelated but complementary 
information and is applicable to all aetiologies. Movement disorders including 
cerebral palsy can be effectively evaluated using these scales.