Clinical Features Indicating Nigrostriatal Dopaminergic Degeneration in Drug-Induced Parkinsonism

Comparative Olfactory Profiles in Parkinson's Disease and Drug-Induced Parkinsonism

OBJECTIVE

Drug-induced parkinsonism (DIP) is a frequently encountered diagnostic possibility when considering Parkinson's disease (PD). While olfactory dysfunction is a common clinical feature in PD, the comparison of olfactory function between the two conditions remains insufficient. This study aimed to compare olfactory function, including threshold, discrimination, and identification (TDI) profiles, between PD and DIP.

METHODS

Consecutive patients with drug-naïve PD (n = 78) or DIP (n = 31) confirmed through dopamine transporter imaging were enrolled in this study. The YSK olfactory function (YOF) test, composed of TDI domains culturally familiar odorants to Koreans, was administered to all patients.

RESULTS

In the study population, patients with DIP were significantly older than patients with PD. Over 70% of patients in each group had hyposmia or anosmia, and there was no significant difference in the occurrence of olfactory dysfunction between the two groups. In addition, there were no differences in the total YOF score and threshold score between the two groups. Meanwhile, the PD group had a significantly lower discrimination and identification score than the DIP group after adjusting for age, sex, the existence of diabetes, disease duration, and cognitive function.

CONCLUSION

This study demonstrated that detailed olfactory profiles are different in PD and DIP, even though olfactory dysfunction can be observed in both conditions.

Retinal Thickness and Its Interocular Asymmetry Between Parkinson's Disease and Drug-Induced Parkinsonism

BACKGROUND

Drug-induced parkinsonism (DIP) is common, but diagnosis is challenging. Although dopamine transporter imaging is useful, the cost and inconvenience are problematic, and an easily accessible screening technique is needed. We aimed to determine whether optical coherence tomography (OCT) findings could differentiate DIP from Parkinson's disease (PD).

METHODS

We investigated 97 de novo PD patients and 27 DIP patients using OCT and [¹⁸F] N-(3-fluoropropyl)-2b-carbon ethoxy-3b-(4-iodophenyl) nortropane (FP-CIT) positron emission tomography. We compared peripapillary retinal nerve fiber layer thickness (pRNFLT) and macular retinal thickness (mRT) between PD and DIP patients as well as interocular differences in the pRNFLT and the mRT. Asymmetric index (%) for retinal thickness (AIRT) was calculated to measure the interocular differences between pRNFLT and mRT. The correlation between AIRT and total striatal specific/non-specific binding ratio asymmetry index (SNBRAI) was investigated in PD and DIP patients.

RESULTS

No significant differences in pRNFLT and mRT values were observed between PD and DIP patients (all P values > 0.090). The mean SNBRAI was significantly higher in PD than in DIP (P = 0.008) patients; however, AIRT did not differ between PD and DIP patients in pRNFLT and mRT (all P values > 0.100). SNBRAI did not correlate with AIRT of pRNFL or mRT in PD and DIP patients (all P values > 0.060).

CONCLUSION

Our study showed no benefit of retinal thickness and interocular asymmetry measurements using OCT for distinguishing PD from DIP in the early stages. Additional investigations are needed for confirmation.

Gait abnormalities and non-motor symptoms predict abnormal dopaminergic imaging in presumed drug-induced Parkinsonism

Drug-induced parkinsonism (DIP) can be clinically indistinguishable from degenerative parkinsonism, and bedside assessments are needed to differentiate between these conditions. We examined 34 U.S. Veterans with DIP using ¹²³I-FP-CIT (DAT-SPECT) to identify underlying nigrostriatal degeneration. Participants were 94% male with mean age of 64.5 ± 7.1 years. DAT-SPECT was abnormal in 12/34 (35%). Comparing normal and abnormal imaging groups, there were no differences in age, sex, race/ethnicity, psychiatric diagnosis, motor severity, or RBD Screening Questionnaire scores. Those with underlying neurodegeneration reported significantly more non-motor symptoms (NMS), worse olfactory function on the University of Pennsylvania Smell Identification Test, and greater turning duration/steps on the instrumented Timed Up and Go. Area under the curve (AUC) combining poor olfaction and total NMS burden was 0.84 (CI 0.71-0.97), while AUC for turn steps was 0.91 (CI 0.81-1.00). Gait impairment, hyposmia, and NMS may be useful alone and in combination to identify DIP patients with underlying dopaminergic degeneration.

Secondary parkinsonism due to drugs, vascular lesions, tumors, trauma, and other insults

In addition to neurodegenerative disorders, there are many secondary forms of parkinsonism. The most common cause for secondary parkinsonism is the intake of distinct drugs. Neuroleptics and calcium channel blockers have been mainly described to induce parkinsonism, but also other drugs were suspected to cause or worsen parkinsonism. Another common cause for secondary parkinsonism are vascular lesions (i.e. vascular parkinsonism). Furthermore, also brain tumors have been described as rare causes for parkinsonism. Moreover, parkinsonism can be caused by chronic traumatic encephalopathy, which is a special case, since secondary insults to the brain leads to the occurrence of a neuropathologically defined disease. Other rare causes for secondary parkinsonism are lesions caused by infectious or immunological diseases as well as toxins or street drugs.

Acute dopamine receptor blockade in substantia nigra pars reticulata: a possible model for drug-induced Parkinsonism

Dopamine (DA) depletion modifies the firing pattern of neurons in the substantia nigra pars reticulata (SNr), shifting their mostly tonic firing toward irregularity and bursting, traits of pathological firing underlying rigidity and postural instability in Parkinson's disease (PD) patients and animal models of Parkinsonism (PS). Drug-induced Parkinsonism (DIP) represents 20-40% of clinical cases of PS, becoming a problem for differential diagnosis, and is still not well studied with physiological tools. It may co-occur with tardive dyskinesia. Here we use in vitro slice preparations including the SNr to observe drug-induced pathological firing by using drugs that most likely produce it, DA-receptor antagonists (SCH23390 plus sulpiride), to compare with firing patterns found in DA-depleted tissue. The hypothesis is that SNr firing would be similar under both conditions, a prerequisite to the proposal of a similar preparation to test other DIP-producing drugs. Firing was analyzed with three complementary metrics, showing similarities between DA depletion and acute DA-receptor blockade. Moreover, blockade of either nonselective cationic channels or Ca_v3 T-type calcium channels hyperpolarized the membrane and abolished bursting and irregular firing, silencing SNr neurons in both conditions. Therefore, currents generating firing in control conditions are in part responsible for pathological firing. Haloperidol, a DIP-producing drug, reproduced DA-receptor antagonist firing modifications. Since acute DA-receptor blockade induces SNr neuron firing similar to that found in the 6-hydroxydopamine model of PS, output basal ganglia neurons may play a role in generating DIP. Therefore, this study opens the way to test other DIP-producing drugs. NEW & NOTEWORTHY Dopamine (DA) depletion enhances substantia nigra pars reticulata (SNr) neuron bursting and irregular firing, hallmarks of Parkinsonism. Several drugs, including antipsychotics, antidepressants, and calcium channel antagonists, among others, produce drug-induced Parkinsonism. Here we show the first comparison between SNr neuron firing after DA depletion vs. firing found after acute blockade of DA receptors. It was found that firing in both conditions is similar, implying that pathological SNr neuron firing is also a physiological correlate of drug-induced Parkinsonism.

Neuroimaging in Parkinson's disease: focus on substantia nigra and nigro-striatal projection

PURPOSE OF REVIEW

The diagnosis of Parkinson disease is based on clinical features; however, unmet need is an imaging signature for Parkinson disease and the early differential diagnosis with atypical parkinsonisms. A summary of the molecular imaging and MRI recent evidences for Parkinson disease diagnosis will be presented in this review.

RECENT FINDINGS

The nigro-striatal dysfunction explored by dopamine transporter imaging is not a mandatory diagnostic criterion for Parkinson disease, recent evidence supported its utility as in-vivo proof of degenerative parkinsonisms, and there might be compensatory mechanisms leading to an early overestimation. The visualization of abnormalities in substantia nigra by MRI has been recently described as sensitive and specific tool for Parkinson disease diagnosis, even in preclinical conditions, whereas it is not useful for distinguishing between Parkinson disease and atypical parkinsonisms. The relationship between the nigral anatomical changes, evaluated as structural alterations or neuromelanin signal decrease and the dopaminergic nigro-striatal function needs to be further clarified.

SUMMARY

With the hopeful advent of potential neuroprotective drugs for PD, it is crucial to have imaging measures that are able to detect at risk subjects. Moreover it is desirable to increase the knowledge about which measure better predicts the probability and the time of clinical conversion to PD.