Figure 1
Flow Chart of the Study Selection Process*.
* Sensory deficits: Five article detected: Two were excluded due to lack of relevance, 2 were review, 1 article was duplicate.
Figure 2
Neuroanatomy of Auditory System.
Table 1
Hearing Impairment Studies Characteristics and Design.
| Study, year | Method of the study/Type of Test | Number of Subjects | Mean Age (y) | Gender M/F | Duration of Tremor (y) | Test Results | P value |
|---|---|---|---|---|---|---|---|
| Ondo et al. 2003 [38] | NHHI -Describing hearing loss (DHL) -Hearing aid usage (HAU) Acoustic immittance measures (tympanogram, crossed and uncrossed acoustic reflexes) Distortion-product otoacoustic emissions Pure tone air-conduction Audiometry Speech audiometry (speech threshold, PBm, SSIm, DSI) Bone-conduction audiometry | 250 ET, 127 PD, 127 HC 74 ET (10 patients excluded because of middle ear disease that was identified during audiometry testing) | 66.2 ± 13.5 65.3 ± 9.6 62.6 ± 11.9 | 138/112 68/59 66/61 | 24.8 ± 17.9 7.9 ± 5.6 NA | Total NHHI scores differed between groups DHL: Scores were highest in the ET group followed by the control group and patients with PD HAU: 16.8% in ET 1.6% in PD 0.8% in HC Higher frequency loss was detected in ET group. | ET vs. HC: <0.001 ET vs PD: <0.001 <0.0001 |
| Louis et al. 2005 [39] | Brain repository study Reported deafness | 94 | 74.1 ± 10.1 | 38/57 | 40 ± 20.3 | 20 (21.3%) of 94 ET cases, including 18 (26.9%) among the 67 participants ≥70.18 patients were using hearing aid. | |
| Benito-Leon et al. 2007 [40] | Population based study, subjects with >65 years’ old Reported hearing impairment | 248 ET 4669 Controls | 75 73 | 104/144 1985/2684 | 5 | 38.7% vs 29.4% After adjustments for age, gender, educational level, and depressive symptoms, there was an association between hearing impairment and ET | 0.002 0.021 OR =1.4 95% CI = 1.05–1.8 |
| Balaban et al. 2011 [42] | Pure tone audiometric test (PTA) Tympanogram Transient-evoked otoacoustic Emissions (TEOAE) Auditory brainstem response (ABR) Bitermal caloric test. | 23 ET 21 HC | 49.4 ± 26.4 51.9 ± 24.1. | 17/6 11/10 | 7.86 ± 6.39 NA | PTA: 30 ± 23.3 vs. 22.5 ± 15.2 The average hearing thresholds at frequencies of 250 and 500 Hz were found to be higher in ET. The TEOAE responses of the ET patients and HC were found significantly different. ABR (I,V peak, I-V interpeak latencies did not differed between groups | <0.05 <0.05 <0.05 >0.05 |
| Benito- Leon et al. 2011 [41] | Reported hearing impairment | 207 ET 2472 Controls | 76.0 75.3 | 99/118 968/1404 | 44.9 vs. 36.3 | <0.05 | |
| Yilmaz et al. 2015 [43] | Described hearing loss by subjects PTA Speech recognition threshold, Tympanogram, Short increment sensitivity index (SISI), Tone decay, TEOAE | 34 ET 45 HC | 57.5 60.0 | 16/18 20/25 | 12 NA | 50% vs. 2.2 The tone decay mean values in 4,000 Hz of the patients’ right ear were significantly higher. The number of patients without OAE was significantly higher than in HC | <0.001 >0.05 >0.05 >0.05 <0.005 <0.05 |
| Ghika et al. 2015 [44] | Assessments was made by using a questionnaire (four questions) | 121 ET 54 ET-PD | 66.9 72.6 | 52/69 24/30 | 13.7 18.4 | 65.3% vs. 28.3% | <0.001 |
[i] NHHI: Nursing Home Hearing Handicap Index.
PBm: Maximum performance for single syllable words SSIm: Synthetic Sentence Index DSI: Dichotic Sentence Index.
Figure 3
Neuroanatomy of Olfactory System.
Table 2
Olfactory Identification Studies Characteristics and Design.
| Study, year | Type of Test | Number of Subjects | Mean Age (y) | Gender M/F | Duration of Tremor (y) | Test Results | P value | |||
|---|---|---|---|---|---|---|---|---|---|---|
| Busenbark et al, 1992 [79] | UPSIT | 16 ET | 36.3 vs.37.2 | 0.19 | ||||||
| 17 HC | ||||||||||
| Louis et al, 2002 [80] | UPSIT | 37 ET | 68.9 | 16/21 | 18.9 | 29.0 ± 6.1 vs | 0.02 | |||
| 37 HC | 67.3 | 18/19 | NA | 31.9 ± 4.6 | ||||||
| Louis et al, 2003 [82] | UPSIT | 13 ET with RT | 73.7 | 7/6 | 24.9 | 29.3 ± 4.3 vs | 0.69 | |||
| 58 ET no RT | 66.6 | 28/30 | 22.0 | 29.4 ± 6.4 | ||||||
| Applegate et al, 2005 [81] | UPSIT | 87 ET | 67.8 | 39/46 | 22.5 | 29.2 ± 6.6 vs. | 0.04 | |||
| 92 HC | 67.1 | 41/51 | NA | 31.3 ± 5.4 | ||||||
| Shah et al, 2008 [84] | UPSIT | 245 HC | 49.5 | 84/161 | NA | 33.0 | ||||
| 64 Tremulous PD | 67.2 | 44/20 | 4.8 | 18.05 | <0.001* | |||||
| 30 Familial ET | 53.1 | 15/15 | 24.2 | 35.0 | <0.001* | |||||
| 29 Non familial ET | 67.3 | 12/17 | 12.4 | 31.0 | 0.67* | |||||
| Louis et al, 2008 [83] | UPSIT | Total 83 ET | 63.7 | 55/38 | 20.7 | 30.5 | 0.09** | |||
| 40 ET with HBHC | 0.002*** | |||||||||
| 43ET with LBHC | ||||||||||
| 69 HC | 63.5 | 31/38 | NA | 31.7 | ||||||
| Djaldetti et al, 2008 [86] | UPSIT | 7 ET | 53 | 8.5 | 23.2 | NSv | ||||
| 17 Mixed tremor | 72 | 15.4 | 21.7 | NS* | ||||||
| 17 PD | 61 | 6.7 | 13.7 | <0.001* | ||||||
| 9 HC | 53 | NA | 27.2 | |||||||
| Silveira-Moriyama et al, 2009 [87] | UPSIT | 21 SWEDD | 65.4 | 10/11 | 9.3 | 27.3 | 0.07* | |||
| 26 ET | 69.0 | 8/18 | 11.4 | 27.9 | 0.4* | |||||
| 16 dystonia | 66.7 | 7/9 | 19.7 | 27.6 | 0.9* | |||||
| 191 PD | 65.6 | 114/77 | 10.2 | 17.6 | <0.001* | |||||
| 136 HC | 64.9 | 72/64 | NA | 29.5 | ||||||
| Quagliato et al. 2009 [85] | UPSIT-12 | 40 ET(21 definite, 11 possible, 8 probable ET) | 59.8 | 17/23 | 17.4 | 9.10 vs. 9.11 | Undetermined | |||
| 89 HC | 56.08 | 34/55 | NA | |||||||
| McKinnon et al. 2010 [88] | UPSIT | 207 HC | 77.0 | 59/158 | UD | 29.7 | <0.001**** >0.05* | |||
| 23 Suspected PD | 80.8 | 11/12 | 28.1 | >0.05** | ||||||
| 15 Possible PD | 81.7 | 7/8 | 27.0 | >0.05 | ||||||
| 19 Probable PD | 71.7 | 12/7 | 20.7 | <0.001* | ||||||
| 37 ET | 79.4 | 20/17 | 31.2 | >0.05* | ||||||
| 25 RLS | 74.5 | 6/19 | 32.7 | >0.05* | ||||||
| 27 MCI | 81.3 | 19/14 | 26.6 | >0.05* | ||||||
| Bradvica et al. 2015 [90] | Pocket Smell Test PST | <0.001**** | ||||||||
| 51 ET | 65.2 | 17/34 | 19.6% | |||||||
| 59 PD | 67.2 | 35/24 | 74.6% | |||||||
| 26 HC | 60.2 | 13/13 | 23.1% | |||||||
| Wu et al. 2016 [89] | Sniffin Sticks (SS-16) | 49 ET | UD | UD | UD | 9.47 | 0.82 | |||
| 79 HC | 9.66 | |||||||||
[i] * Comparing HC.
** Comparison of transformed UPSIT score.
*** Comparison of HBHC and LBHC groups.
**** For null hypothesis.
ET: Essential tremor, HC: Healthy controls, NA: Not applicable, RT: Resting tremor, PD: Parkinson’s Disease, HBHC: High blood harmane concentration, LBHC: Low blood harmane concentration, NS: Not significant, RLS: Restless legs syndrome, MCI: Mild cognitive impairment.