LAUSR

Clinical phenomenology is the first step to generate a differential diagnosis. In the case presented by Desai et al., the diagnostic reasoning from the phenomenological observations changed after the results from paraclinical investigations. The clinical features included a combination of segmental dystonia, oculogyric crises (OGC), jerky movements of the fingers suggesting myoclonus, and muscle atrophy. Since parkinsonism was not particularly evident in the video, the discussant’s differential diagnosis centered on the combination of dystonia, OGC and myoclonus. But the results of the investigations changed everything. The EMG revealed evidence of motor neuron disease (MND) and a DAT Scan was abnormal. After these results, the differential diagnosis shifted to disorders that can cause juvenile parkinsonism, dystonia and MND such as variant ataxia-telangiectasia, ATP1A3, SCA2, DJ1 and others. Consanguinity suggested an autosomal recessive disorder and whole exome sequencing (WES) revealed a novel homozygous mutation in the DJ1 gene. This novel case was very humbling and, thus, highly instructive. It emphasizes the value of EMG in jerky movement disorders; the tremulous movements of the fingers represented minipolymyoclonus, an expression of MND. It also serves to highlight the limitations of conclusions reached from phenomenological observations alone. Since there was little if any clinical parkinsonism and no benefit from levodopa, juvenile parkinsonism was not considered in the initial differential diagnosis. Yet, it was ultimately the DAT Scan that pointed towards the correct diagnostic category; this case suggests that it might be worth obtaining a DAT Scan in the absence of parkinsonism in selected unusual movement disorders. Although whole exome sequencing can misguide us by revealing variants of unknown significance, in this case, exome sequencing was key. Another curious twist in this case is that oculogyric crises feature prominently in dopa-responsive dystonia, in which a DAT scan is normal and the response to L-dopa is usually marked—the opposite of what was observed in this case.