A scan without evidence is not evidence of absence: Scans without evidence of dopaminergic deficit in a symptomatic leucine-rich repeat kinase 2 mutation carrier.

Further evidence that radio-tracer imaging can be normal despite the presence of clear motor signs perhaps due to early compensatory mechanisms...

Mov Disord. 2015 Dec 21. doi: 10.1002/mds.26450. [Epub ahead of print]

Wile DJ, Dinelle K, Vafai N, McKenzie J, Tsui JK, Schaffer P, Ding YS, Farrer M, Sossi V, Stoessl AJ.

INTRODUCTION:

The basis for SWEDD is unclear, with most cases representing PD mimics but some later developing PD with a dopaminergic deficit.

METHODS:

We studied a patient initially diagnosed with SWEDD (based on 18 F-dopa PET) who developed unequivocal PD associated with a leucine-rich repeat kinase 2 p.G2019S mutation. Repeat multitracer PET was performed at 17 years' disease duration, including (+)[11C]dihydrotetrabenazine, [11C](N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine (which binds the serotonin transporter), and 18 F-dopa.

RESULTS:

The patient showed bilateral striatal dopaminergic denervation (right putamen 28% of age-matched normal, left putamen 33%). 18 F-dopa uptake was decreased, particularly on the left (mean 31% of normal vs. 45% on the more affected right side). Serotonin transporter binding was relatively preserved in the putamen (right mean 90% of normal, left 81%) and several cortical regions.

CONCLUSIONS:

SWEDD can occur in genetically determined PD and may, in some cases, be the result of compensatory nondopaminergic mechanisms operating in early disease.