On 2014 Aug 13, David Keller commented:

Smoking reduces risk of PD, but increases risk of COPD and of vascular Parkinsonism

It is well established that smoking is a major risk factor for COPD. Smoking has also been shown to reduce the risk of Parkinson disease (1), thought to be due to neuroprotection by nicotine (2). Therefore, based on the prior observed associations with smoking, one would expect the risk of PD to be lower in COPD patients than in patients with no smoking history. I propose that the unexpected association between COPD and PD may be due to misdiagnosis of vascular Parkinsonism as PD.

Smoking is a major risk factor for COPD and for atherosclerotic vascular disease (ASVD). Parkinsonism can be caused by ASVD, in which case it is categorized as vascular Parkinsonism (VP), a disease distinct from classic neurodegenerative PD. VP would be expected to correlate directly with COPD, while PD should be inversely correlated with COPD, based on the known association of smoking with ASVD, and its inverse association with PD.

COPD is expected to be associated with vascular Parkinsonism, but not with Parkinson's disease, based on the known relationships of these diseases with smoking. The results of this study would be consistent with these known associations if enough VP patients were misdiagnosed as having PD. I suggest that the data be re-examined to consider this possibility.

Lastly, the authors refer to dementia as a neurodegenerative disease. Dementia is actually a symptom which can be caused by neurodegenerative diseases (such as Alzheimer's disease or dementia with Lewy bodies), atherosclerotic disease (as in multi-infarct vascular dementia), other disorders, or a combination thereof. It is incorrect to categorize dementia due to atherosclerotic infarctions as a "neurodegenerative disorder".

References

1: van der Mark M, Nijssen PC, Vlaanderen J, Huss A, Mulleners WM, Sas AM, van Laar T, Kromhout H, Vermeulen R. A case-control study of the protective effect of alcohol, coffee, and cigarette consumption on Parkinson disease risk: time-since-cessation modifies the effect of tobacco smoking. PLoS One. 2014 Apr 30;9(4):e95297. doi: 10.1371/journal.pone.0095297. eCollection 2014. PubMed PMID: 24788751; PubMed Central PMCID: PMC4005732.

2: Ross GW, Petrovitch H. Current evidence for neuroprotective effects of nicotine and caffeine against Parkinson's disease. Drugs Aging. 2001;18(11):797-806. Review. PubMed PMID: 11772120.

On 2014 Aug 13, David Keller commented:

Smoking reduces risk of PD, but increases risk of COPD and of vascular Parkinsonism

It is well established that smoking is a major risk factor for COPD. Smoking has also been shown to reduce the risk of Parkinson disease (1), thought to be due to neuroprotection by nicotine (2). Therefore, based on the prior observed associations with smoking, one would expect the risk of PD to be lower in COPD patients than in patients with no smoking history. I propose that the unexpected association between COPD and PD may be due to misdiagnosis of vascular Parkinsonism as PD.

Smoking is a major risk factor for COPD and for atherosclerotic vascular disease (ASVD). Parkinsonism can be caused by ASVD, in which case it is categorized as vascular Parkinsonism (VP), a disease distinct from classic neurodegenerative PD. VP would be expected to correlate directly with COPD, while PD should be inversely correlated with COPD, based on the known association of smoking with ASVD, and its inverse association with PD.

COPD is expected to be associated with vascular Parkinsonism, but not with Parkinson's disease, based on the known relationships of these diseases with smoking. The results of this study would be consistent with these known associations if enough VP patients were misdiagnosed as having PD. I suggest that the data be re-examined to consider this possibility.

Lastly, the authors refer to dementia as a neurodegenerative disease. Dementia is actually a symptom which can be caused by neurodegenerative diseases (such as Alzheimer's disease or dementia with Lewy bodies), atherosclerotic disease (as in multi-infarct vascular dementia), other disorders, or a combination thereof. It is incorrect to categorize dementia due to atherosclerotic infarctions as a "neurodegenerative disorder".

References

1: van der Mark M, Nijssen PC, Vlaanderen J, Huss A, Mulleners WM, Sas AM, van Laar T, Kromhout H, Vermeulen R. A case-control study of the protective effect of alcohol, coffee, and cigarette consumption on Parkinson disease risk: time-since-cessation modifies the effect of tobacco smoking. PLoS One. 2014 Apr 30;9(4):e95297. doi: 10.1371/journal.pone.0095297. eCollection 2014. PubMed PMID: 24788751; PubMed Central PMCID: PMC4005732.

2: Ross GW, Petrovitch H. Current evidence for neuroprotective effects of nicotine and caffeine against Parkinson's disease. Drugs Aging. 2001;18(11):797-806. Review. PubMed PMID: 11772120.