Abstract
Introduction
Up to 18% of people in industrialised societies are mildly affected by chronic tinnitus, and 0.5% report tinnitus having a severe effect on their daily life. Tinnitus can be associated with hearing loss, acoustic neuromas, drug toxicity, ear diseases, and depression. Tinnitus can last for many years, and can interfere with sleep and concentration.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments for chronic tinnitus? We searched: Medline, Embase, The Cochrane Library, and other important databases up to November 2013 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 33 studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review, we present information relating to the effectiveness and safety of the following interventions: acamprosate, acupuncture, antidepressant drugs, benzodiazepines, carbamazepine, electromagnetic stimulation, ginkgo biloba, hearing aids, hypnosis, psychotherapy, tinnitus-masking devices, and cognitive behavioural therapy plus tinnitus-masking device (tinnitus retraining therapy).
Key Points
Up to 18% of people in industrialised societies are mildly affected by chronic tinnitus, and 0.5% report tinnitus having a severe effect on their daily life.
Tinnitus can be associated with hearing loss, acoustic neuromas, drug toxicity, ear diseases, or depression.
Tinnitus can last for many years, and can interfere with sleep and concentration.
We found insufficient evidence to show that antidepressant drugs improve tinnitus symptoms.
Antidepressant drugs can improve depression in people with tinnitus.
Tricyclic antidepressants (TCAs) are associated with adverse effects such as dry mouth, blurred vision, and constipation.
Psychotherapy (CBT) may be no more effective than placebo at reducing tinnitus loudness, but it may improve overall symptoms of tinnitus at 12 months.
CBT may be more effective at improving anxiety, depression, quality of life, and annoyance scores for people with tinnitus.
We don't know whether CBT plus a tinnitus masking device is more effective than waiting-list control at improving depression or tinnitus annoyance scores in people with tinnitus.
We don't know whether benzodiazepines, acupuncture, hypnosis, electromagnetic stimulation, hearing aids, or tinnitus-masking devices are effective in people with tinnitus.
Gingo biloba may be no more effective than placebo at improving overall symptoms of tinnitus at 3 months. However, evidence was limited and inconsistent.
Acamprosate may be more effective than placebo at improving overall symptom scores at 3 months in people with tinnitus. However, evidence was weak, and it is unclear whether the improvement was clinically important.
Carbamazepine may be no more effective than placebo at improving symptoms of tinnitus, and is associated with adverse effects such as dizziness, nausea, and headache.
About this condition
Definition
Tinnitus is the perception of sound in the ear or head that does not arise from the external environment, from within the body (e.g., vascular sounds), or from auditory hallucinations related to mental illness. This review is concerned with tinnitus for which tinnitus is the only, or the predominant, symptom in an affected person.
Incidence/ Prevalence
Up to 18% of the general population in industrialised countries are mildly affected by chronic tinnitus, and 0.5% report tinnitus having a severe effect on their ability to lead a normal life.
Aetiology/ Risk factors
Tinnitus can occur as an isolated idiopathic symptom, or in association with any type of hearing loss. Tinnitus can be a particular feature of presbycusis (age-related hearing loss), noise-induced hearing loss, Menière's disease (see review on Menière's disease), or the presence of an acoustic neuroma. In people with toxicity from aspirin or quinine, tinnitus can occur with hearing thresholds remaining normal. Tinnitus is also associated with depression, although it can be unclear whether the tinnitus is a manifestation of the depressive illness or a factor contributing to its development. Studies involving people with tinnitus caused by Menière's disease, acoustic neuroma, chronic otitis media, head injury, barotraumas, or other clear pathology have been excluded from this review. This review is principally concerned with idiopathic tinnitus with or without degenerative sensorineural hearing loss.
Prognosis
Tinnitus can have an insidious onset, with a long delay before clinical presentation. It can persist for many years or decades, particularly when associated with a sensorineural hearing loss. Tinnitus can cause disruption of sleep patterns, an inability to concentrate, and depression.
Aims of intervention
To reduce the loudness and intrusiveness of the tinnitus, and to reduce its impact on daily life, with minimum adverse effects of treatment.
Outcomes
Resolution of tinnitus; improvement in tinnitus (includes tinnitus loudness [assessed by a visual analogue scale or symptom scores]); impact of tinnitus on quality of life, as measured by estimates of interference with activities of daily life or with emotional state; and adverse effects.
Methods
Clinical Evidence search and appraisal November 2013. The following databases were used to identify studies for this systematic review: Medline 1966 to November 2013, Embase 1980 to November 2013, and The Cochrane Database of Systematic Reviews 2013, issue 11 (1966 to date of issue). Additional searches were carried out in the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA) database. We also searched for retractions of studies included in the review. Titles and abstracts identified by the initial search, run by an information specialist, were first assessed against predefined criteria by an evidence scanner. Full texts for potentially relevant studies were then assessed against predefined criteria by an evidence analyst. Studies selected for inclusion were discussed with an expert contributor. All data relevant to the review were then extracted by an evidence analyst. Study design criteria for inclusion in this review were: published RCTs and systematic reviews of RCTs in the English language, at least single-blinded, and containing at least 20 individuals, of whom at least 80% were followed up. There was no minimum length of follow-up required to include studies. We excluded all studies described as 'open', 'open label', or not blinded unless blinding was impossible. We included RCTs and systematic reviews of RCTs where harms of an included intervention were assessed, applying the same study design criteria for inclusion as we did for benefits. In addition, we use a regular surveillance protocol to capture harms alerts from organisations such as the FDA and the MHRA, which are added to the reviews as required. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).
Table.
GRADE Evaluation of interventions for Tinnitus.
Important outcomes | Impact of tinnitus on quality of life, Impact on quality of life, Improvement in tinnitus, Resolution of tinnitus | ||||||||
Studies (Participants) | Outcome | Comparison | Type of evidence | Quality | Consistency | Directness | Effect size | GRADE | Comment |
What are the effects of treatments for chronic tinnitus? | |||||||||
2 (90) | Improvement in tinnitus | Acamprosate versus placebo | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and no intention-to-treat analysis; directness point deducted for no statistical analysis between groups in one RCT |
1 (40) | Impact of tinnitus on quality of life | Acamprosate versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
6 (222) | Improvement in tinnitus | Acupuncture versus sham acupuncture | 4 | –1 | –1 | 0 | 0 | Low | Quality points deducted for incomplete reporting of results; consistency point deducted for conflicting results |
2 (104) | Impact of tinnitus on quality of life | Acupuncture versus sham acupuncture | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
4 (278) | Improvement in tinnitus | Tricyclic antidepressants (TCAs) versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for incomplete reporting of results; directness point deducted for no statistical analysis between groups in one RCT |
1 (117) | Impact of tinnitus on quality of life | Tricyclic antidepressants (TCAs) versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
2 (196) | Improvement in tinnitus | Seretonin selective re-uptake inhibitors (SSRIs) versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data; directness point deducted for inclusion of a co-intervention in 1 RCT (oxazepam) |
1 (76) | Impact of tinnitus on quality of life | Seretonin selective re-uptake inhibitors (SSRIs) versus placebo | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and RCT being underpowered to detect a clinically meaningful difference between groups; directness point deducted for inclusion of a co-intervention (oxazepam) |
1 (85) | Improvement in tinnitus | Serotonin antagonist and re-update inhibitor (SARI) versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
1 (85) | Impact of tinnitus on quality of life | Serotonin antagonist and re-update inhibitor (SARI) versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
2 (70) | Improvement in tinnitus | Benzodiazepines versus placebo | 4 | –3 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data, incomplete reporting of results, and flaws with blinding in 1 RCT; directness point deducted for lack of inert placebo in crossover RCT |
5 (271) | Improvement in tinnitus | Electromagnetic stimulation versus placebo | 4 | –2 | –1 | 0 | 0 | Very low | Quality points deducted for incomplete reporting of results, and other methodological flaws; consistency point deducted for conflicting results |
1 (66) | Impact of tinnitus on quality of life | Electromagnetic stimulation versus placebo | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and incomplete reporting of results; directness point deducted for no statistical analysis between groups |
3 (1144) | Improvement in tinnitus | Ginkgo biloba versus placebo | 4 | –2 | –1 | 0 | 0 | Very low | Quality points deducted for incomplete reporting of results and other methodological flaws; consistency point deducted for conflicting results |
1 (100) | Impact of tinnitus on quality of life | Ginkgo biloba versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
1 (39) | Improvement in tinnitus | Hearing aids versus waiting list control | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
1 (92) | Improvement in tinnitus | Hypnosis versus counselling | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and incomplete reporting of results; directness point deducted for inclusion of only those who were suggestible to hypnosis |
19 (1279) | Improvement in tinnitus | CBT versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality point deducted for methodological flaws of one review and incomplete reporting of results |
at least 12 (at least 1158) | Impact of tinnitus on quality of life | CBT versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for incomplete reporting of results and methodological flaws of one review |
1 (99) | Impact of tinnitus on quality of life | Acceptance and commitment therapy (ACT) versus waiting-list control | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomple reporting of results |
1 (21) | Improvement in tinnitus | Tinnitus-masking devices versus placebo | 4 | –3 | 0 | 0 | 0 | Very low | Quality points deducted for sparse data, no blinding, incomplete reporting of results, and other methodological flaws (reporting of post-crossover results) |
1 (90) | Impact on quality of life | CBT plus a tinnitus-masking device versus waiting-list control | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and incomplete reporting of results; directness point deducted for the addition of CBT in the control group at 10 months |
1 (48) | Improvement in tinnitus | Carbamazepine versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.
Glossary
- Low-quality evidence
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
- Masking device
A small device similar to a behind-the-ear hearing aid that produces a broad frequency noise. It is thought to hide the noise of the tinnitus.
- Menière's disease
A condition characterised by episodic vertigo, tinnitus, and sensorineural hearing loss.
- Presbycusis
Age-related hearing loss.
- Tinnitus Handicap Inventory
A questionnaire assessing the impact of tinnitus on the subject's quality of life.
- Tinnitus retraining therapy
A combination of cognitive behavioural therapy and tinnitus masking, highly tailored to individual people.
- Very low-quality evidence
Any estimate of effect is very uncertain.
Disclaimer
The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients. To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.
Contributor Information
Julian Savage, Université de Sherbrooke Québec, Canada.
Angus Waddell, Great Western Hospital, Swindon, UK.
References
- 1.Coles RR. Epidemiology of tinnitus: (1) prevalence. J Laryngol Otol 1984;9(suppl):7–15. [DOI] [PubMed] [Google Scholar]
- 2.Sullivan MD, Katon W, Dobie R, et al. Disabling tinnitus: association with affective disorder. Gen Hosp Psychiatry 1988;10:285–291. [DOI] [PubMed] [Google Scholar]
- 3.Zoger S, Svedlund J, Holgers KM. Psychiatric disorders in tinnitus patients without severe hearing impairment: 24 month follow-up of patients at an audiological clinic. Audiology 2001;40:133–140. [DOI] [PubMed] [Google Scholar]
- 4.Pichora-Fuller MK, Santaguida P, Hammill A, et al; Agency for Healthcare Research and Quality. Evaluation and treatment of tinnitus: comparative effectiveness. August 2013. Available at http://effectivehealthcare.ahrq.gov/search-for-guides-reviews-and-reports/?pageaction=displayproduct&productid=1650 (accessed on 25 July 2014). [PubMed] [Google Scholar]
- 5.Sharma DK, Kaur S, Singh J, et al. Role of acamprosate in sensorineural tinnitus. Ind J Pharmacol 2012;44:93–96. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Azevedo AA, Figueiredo RR. Tinnitus treatment with acamprosate: double-blind study. Rev Bras Otorhinolaringol 2005;71:618–623. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Kim JI, Choi JY, Lee DH, et al. Acupuncture for the treatment of tinnitus: a systematic review of randomized clinical trials. BMC Complement Altern Med 2012;12:97. Search date 2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Rogha M, Rezvani M, Khodami AR. The effects of acupuncture on the inner ear originated tinnitus. J Res Med Sci 2011;16:1217–1223. [PMC free article] [PubMed] [Google Scholar]
- 9.Hoare DJ, Kowalkowski VL, Kang S, et al. Systematic review and meta-analyses of randomized controlled trials examining tinnitus management. Laryngoscope 2011;121:1555–1564. Search date 2010. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Baldo P, Doree C, Molin P, et al. Antidepressants for patients with tinnitus. In: The Cochrane Library, Issue 11; 2013. Chichester, UK: John Wiley & Sons, Ltd. Search date 2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Sullivan M, Katon W, Russo J, et al. A randomised trial of nortriptyline for severe chronic tinnitus. Arch Intern Med 1993;153:2251–2259. [PubMed] [Google Scholar]
- 12.Bayar N, Boke B, Turan E, et al. Efficacy of amitriptyline in the treatment of subjective tinnitus. J Otolaryngol 2001;30:300–303. [DOI] [PubMed] [Google Scholar]
- 13.Mihail RC, Crowley JM, Walden BE, et al. The tricyclic trimipramine in the treatment of subjective tinnitus. Ann Otolo Rhinol Laryngol 1988;97:120–123. [DOI] [PubMed] [Google Scholar]
- 14.Podoshin L, Ben-David Y, Fradis M, et al. Idiopathic subjective tinnitus treated by amitryptiline hydrochloride/biofeedback. Int Tinnitus J 1995;1:54–60. [PubMed] [Google Scholar]
- 15.Robinson SK, Viirre ES, Bailey KA, et al. Randomised placebo-controlled trial of a selective serotonin reuptake inhibitor in the treatment of nondepressed tinnitus subjects. Psychosom Med 2005;67:981–988. [DOI] [PubMed] [Google Scholar]
- 16.Zoger S, Svedlund J, Holgers KM. The effects of sertraline on severe tinnitus suffering - a randomized, double-blind, placebo-controlled study. J Clin Psychopharmacol 2006;26:32–39. [DOI] [PubMed] [Google Scholar]
- 17.Holgers KM, Zoger S, Svedlund J. The impact of sertraline on health-related quality of life in severe refractory tinnitus: a double-blind, randomized, placebo-controlled study. Audiol Med 2011;9:67–72. [Google Scholar]
- 18.Dib GC, Kasse CA, ves de Andrade T, et al. Tinnitus treatment with Trazodone. Brasileira J Otorrinolaringologia 2007;73:390–397. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Schilter B, Jager B, Heerman R, et al. Pharmacological and psychological treatment options in chronic subjective tinnitus: a meta-analysis of effective treatments. HNO 2000;48:589–597. Search date 1995. [DOI] [PubMed] [Google Scholar]
- 20.Johnson RM, Brummett R, Schleuning A. Use of alprazolam for relief of tinnitus. A double-blind study. Arch Otolaryngol Head Neck Surg 1993;119:842–845. [DOI] [PubMed] [Google Scholar]
- 21.Jalali MM, Kousha A, Naghavi SE, et al. The effects of alprazolam on tinnitus: a cross-over randomized clinical trial. Med Sci Monit 2009;15:I55–I60. [PubMed] [Google Scholar]
- 22.Meng Z, Liu S, Zheng Y, et al. Repetitive transcranial magnetic stimulation for tinnitus. In: The Cochrane Library, Issue 11, 2013. Chichester, UK: John Wiley & Sons, Ltd. Search date May 2011. 21975776 [Google Scholar]
- 23.Peng Z, Chen XQ, Gong SS. Effectiveness of repetitive transcranial magnetic stimulation for chronic tinnitus: a systematic review. Otolaryngol Head Neck Surg (US) 2012;147:817–825. Search date 2012. [DOI] [PubMed] [Google Scholar]
- 24.Dobie RA, Hoberg KE, Rees TS. Electrical tinnitus suppression: a double-blind crossover study. Otolaryngol Head Neck Surg 1986;95:319–333. [DOI] [PubMed] [Google Scholar]
- 25.Roland NJ, Hughes JB, Daley MB, et al. Electromagnetic stimulation as a treatment of tinnitus: a pilot study. Clin Otolaryngol 1993;18:278–281. [DOI] [PubMed] [Google Scholar]
- 26.Hilton M, Zimmerman EF, Hunt WT. Ginkgo biloba for tinnitus. In: The Cochrane Library, Issue 11, 2013. Chichester, UK: John Wiley & Sons, Ltd. Search date 2012. 23543524 [Google Scholar]
- 27.von Boetticher A. Ginkgo biloba extract in the treatment of tinnitus: a systematic review. Neuropsychiatr Dis Treat 2011;7:441–447. Search date 2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Morgenstern C, Biermann E. Long-term treatment of tinnitus with the special gingko extract, Egb 761. Fortschr Med 1997;115:57–58. [In German] [Google Scholar]
- 29.Drew S, Davies E. Effectiveness of ginkgo biloba in treating tinnitus: double blind, placebo controlled trial. BMJ 2001;322:73–75. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30.Rejali D, Sivakumar A, Balaji N. Ginkgo biloba does not benefit patients with tinnitus: a randomized placebo-controlled double-blind trial and meta-analysis of randomized trials. Clin Otolaryngol Allied Sci 2004;29:226–231. [DOI] [PubMed] [Google Scholar]
- 31.Meyer B. A multicentre, randomized, double-blind drug versus placebo study of Ginkgo biloba extract in the tratment of tinnitus. Presse Med 1986;15:1562–1564. [In French] [PubMed] [Google Scholar]
- 32.Melin L, Scott B, Lindberg P, et al. Hearing aids and tinnitus – an experimental group study. Br J Audiol 1987;21:91–97. [DOI] [PubMed] [Google Scholar]
- 33.Mason JD, Rogerson DR, Butler JD. Client centred hypnotherapy in the management of tinnitus — is it better than counselling? J Laryngol Otol 1996;110:117–120. [DOI] [PubMed] [Google Scholar]
- 34.Andersson G, Lyttkens L. A meta-analytic review of psychological treatments for tinnitus. Br J Audiol 1999;33:201–210. Search date 1998. [DOI] [PubMed] [Google Scholar]
- 35.Hesser H, Weise C, Westin VZ, et al. A systematic review and meta-analysis of randomized controlled trials of cognitive-behavioral therapy for tinnitus distress. Clin Psychol Rev 2011;31:545–553. Search date 2009. [DOI] [PubMed] [Google Scholar]
- 36.Martinez Devesa P, Waddell A, Perera R, et al. Cognitive behavioural therapy for tinnitus. In: The Cochrane Library, Issue 11, 2013. Chichester, UK: John Wiley & Sons, Ltd. Search date 2010. 20824844 [Google Scholar]
- 37.Cima RF, Maes IH, Joore MA, et al. Specialised treatment based on cognitive behaviour therapy versus usual care for tinnitus: a randomised controlled trial. Lancet 2012;379:1951–1959. [DOI] [PubMed] [Google Scholar]
- 38.Dobie RA. A review of randomized clinical trials in tinnitus. Laryngoscope 1999;109:1202–1211. Search date 1998. [DOI] [PubMed] [Google Scholar]
- 39.Stephens SDG, Corcoran AL. A controlled study of tinnitus masking. Br J Audiol 1985;19:159–167. [DOI] [PubMed] [Google Scholar]
- 40.Erlandsson S, Ringdahl A, Hutchins T, et al. Treatment of tinnitus: a controlled comparison of masking and placebo. Br J Audiol 1987;21:37–44. [DOI] [PubMed] [Google Scholar]
- 41.Hoekstra CEL, Rynja SP, van Zanten GA, et al. Anticonvulsants for tinnitus. In: The Cochrane Library, Issue 11, 2013. Chichester, UK: John Wiley & Sons, Ltd. Search date 2010. 21735419 [Google Scholar]
- 42.Hulshof JH, Vermeij P. The value of carbamazepine in the treatment of tinnitus. ORL J Otorhinolaryngol Relat Spec 1985;47:262–266. [DOI] [PubMed] [Google Scholar]