• Helen Ling, Seamus Kearney, Helen Lai Kuen Yip, Laura Silveira-Moriyama, Tamas Revesz, Janice L Holton, Catherine Strand, Karen Davey, Kin Ying Mok, James M Polke, and Andrew J Lees.
• Reta Lila Weston Institute of Neurological Studies, UCL Institute of Neurology, London, UK Queen Square Brain Bank for Neurological Disorders, UCL Institute of Neurology, London, UK.
• J. Neurol. Neurosurg. Psychiatr. 2016 Jun 1; 87 (6): 633-41.

ObjectiveTo describe 5 cases of Parkinson's disease lacking any detectable histopathology.BackgroundThe diagnosis of Parkinson's disease is supported histologically by the findings of α-synuclein immunopositive Lewy bodies and neurites and severe substantia nigra cell loss. Bradykinesia as defined by slowness of initiation of movement and a progressive reduction in speed and amplitude on finger tapping is a clinical correlate of pars compacta nigral degeneration. There are very few published cases of Parkinson's disease in which no pathological abnormality was found, and some of these cases were in hindsight thought to have probably been cases of indeterminate senile tremor or dystonic tremor.MethodsRetrospective case notes review of the Queen Square Brain Bank archival collection and detailed neuropathological analysis of the selected cases.Results5 cases considered to have Parkinson's disease by neurologists throughout the entirety of their illness that lacked any histopathological findings known to be associated with Parkinson's syndromes were identified out of a total number of 773 brains with a final clinical diagnosis of Parkinson's disease in the Queen Square Brain Bank. Retrospective case note analysis did not suggest dystonic tremor or indeterminate tremor in any of them. There was a reduction in tyrosine hydroxylase (TH) density in the striatum in these cases when compared with healthy controls, but not in the substantia nigra.ConclusionsStriatal dopamine deficiency without nigral cell loss is the most likely explanation for the clinical findings; other possible explanations include slowness due to comorbidities misinterpreted as bradykinesia, a tardive syndrome related to undisclosed previous neuroleptic exposure, or 'soft age-related' parkinsonian signs. These cases emphasise the need to regularly review the diagnosis in cases of suspected Parkinson's disease and highlight the need for precision in the neurological examination particularly of elderly patients. These cases may represent a distinct entity of diagnostic exclusion and may be considered one explanation for the radiological phenomenon of SWEDD (scans without evidence of dopaminergic deficit).Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

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