Introduction
Tinnitus is the perception of sound without any known external audible source.Reference Nemholt, Schmidt, Wedderkopp and Baguley1–Reference Tunkel, Bauer, Sun, Rosenfeld, Chandrasekhar and Cunningham3 It can affect one or both ears. Disease prevalence has been reported as 10–15 per cent in different series, rising to 33 per cent in patients aged over 60 years. Tinnitus is evaluated as being either subjective or objective. Objective tinnitus is a sound which can be heard by other people, which may be caused by internal body sound or vibration. Subjective tinnitus is the perception of sound without any acoustic, electrical or external stimulation.Reference Pinto, Marcelos, Mezzasalma, Osterne, de Melo Tavares de Lima and Nardi4 Medical support is required by 20 per cent of patients with tinnitus as it can have an adverse effect on daily life, causing cognitive and emotional problems, and issues with communication and sleeping.Reference Nemholt, Schmidt, Wedderkopp and Baguley1, Reference Liu, Han, Li and Yu2 Tinnitus is not a disease in itself, but may be a symptom of various diseases or aggravating co-factors. It can be bothersome and depressing, and may lead to physiological and functional problems.Reference Liu, Han, Li and Yu2
The aetiology of tinnitus is controversial. It can be caused by disorders involving the outer, middle or inner ear, or auditory nerve. Tinnitus is associated with many possible factors, including otological, neurological, infectious, drug-related and physiological disorders.Reference Zhang5, Reference Chan6 However, the exact aetiology is often unclear. In such patients, it is presumed that the production of sound without an external stimulus arises from aberrant neural activity at any point along the pathway from the cochlear apparatus to the auditory cortex.Reference Eggermont7
Platelets are one of the main cells of the blood. These disc-shaped cells play a key part in maintaining the integrity of blood vessels and contribute to haemostasis. Normal platelet counts range between 150 000 and 400 000 per mm3 of blood. Their size and haemostatic potential may differ.Reference Frojmovic and Milton8 The average size of platelets is referred to as mean platelet volume.Reference Sahin, Gur, Elbasan, Yıldırım, Akıllı and Koyunsever9, Reference Kemal, Müderris, Sevil and Kutlar10 Platelets secrete and express a large number of substances that are critical mediators of clotting. Larger platelets may include more granules, and they produce greater amounts of vasoactive and thrombotic factors, which means greater haemostatic activity. Therefore, it is clear that bigger platelets mean better haemostasis.Reference Vizioli, Muscari and Muscari11 Mean platelet volume is affected by smoking, diabetes mellitus, hypercholesterolaemia, hypertension and obesity.Reference Bath and Butterworth12–Reference Coban, Ozdogan, Yazicioglu and Akcit16
This study aimed to determine the effect of mean platelet volume on tinnitus.
Materials and methods
Approval for the study was granted by the Local Ethics Committee of Ankara Yıldırım Beyazıt University, Turkey. This retrospective study was conducted at Ankara Atatürk Hospital and Samsun Ondokuz Mayıs University Hospital, Turkey, between January 2013 and January 2014. A total of 86 patients with tinnitus and 84 healthy subjects were included in the study. The same numbers of patients (43 and 43) and control subjects (42 and 42) were enrolled from the two separate centres. The healthy control group subjects were selected from patients presenting at the clinic for a routine check-up.
All patients underwent physical examination, and those with chronic diseases, bleeding disorders, a history of hypertension, acute infection or diabetes mellitus were excluded. All patients also underwent otomicroscopy and audiological examination (audiogram and tympanogram), to rule out acute or chronic ear problems that may cause tinnitus. Patients and control subjects with a hearing threshold worse than 20 dB at any frequency in the audiogram were excluded from the study. To rule out acute or chronic inflammatory diseases, blood parameters such as C-reactive protein (CRP) and white blood cells (WBC) were checked, and any patients with raised levels of CRP or WBC were excluded. All patients were under 50 years old in order to avoid any effect of presbycusis and tinnitus by presbycusis.
Mean platelet volume parameters were examined and compared between the two (study and control) groups. In our laboratory, the normal value for mean platelet volume was considered as between 6 and 11 μm3.
SPSS software (version 15.0; SPSS, Chicago, Illinois, USA) was used to perform the statistical analyses. All parameters were expressed as mean ± standard deviation. The distribution of normality was evaluated using the Shapiro–Wilk test. The Mann–Whitney U test was used to compare the differences between the control subjects and tinnitus patients. A value of p < 0.05 was considered statistically significant.
Results
The mean age of the study group patients was 33.58 ± 11.65 years and the mean age of the control group subjects was 32.24 ± 10.18 years. The study group consisted of 46 males (53.49 per cent) and 40 females (46.51 per cent), and the control group comprised 36 males (42.86 per cent) and 48 females (57.14 per cent) (Table I).
Descriptive statistics
Data represent means ± standard deviations, unless indicated otherwise.
No statistically significant difference was found between the groups in terms of age and WBC levels (p > 0.05). Mean platelet volume was determined as 7.67 ± 0.83 μm3 in the study group and 7.28 ± 0.56 μm3 in the control group; the difference was found to be statistically significant (p < 0.05).
Discussion
To the best of our knowledge, this is the first study to demonstrate a relationship between mean platelet volume and tinnitus.
Mean platelet volume is one of the parameters indicating platelet function.Reference Park, Schoene and Harris17, Reference Boos and Lip18 Platelets are heterogeneous in size, and large platelets have more granules, more glycoprotein Ib and IIa/IIIa, and more thromboxane A2 level receptors. This means platelet aggregation will be more rapid.Reference Varol, Aksoy, Ozaydin, Erdogan and Dogan19–Reference Jakubowski, Thompson, Vaillancourt, Valeri and Deykin21
Higher mean platelet volume has been reported to be associated with many diseases. Mean platelet volume is a useful marker in the pathophysiology of several conditions such as coronary heart disease and endothelial dysfunction.Reference Balta, Demirkol, Yildizoglu, Arslan, Unlu and Celik22, Reference Kemal, Demirağ, Ekiz and Yücel23 Mean platelet volume is also affected by thyroid and rheumatic diseases, malignancy, and medications.Reference Yazici, Yazici, Erer, Calik, Ozhan and Ataoglu24 There is a negative correlation between mean platelet volume and Crohn's disease, ulcerative colitis and pulmonary diseases.Reference Douda, Bures, Rejchrt, Kopácová, Pecka and Malý25–Reference Ulasli, Ozyurek, Yilmaz and Ulubay27
Mean platelet volume is a simple parameter to determine, but clinical usage of the parameter has not yet been fully accepted. In this study, to determine the effective parameters, the history of all the patients and control subjects was examined. Any patients or healthy subjects with additional diseases, or acute or chronic inflammatory conditions (such as high WBC or CRP levels), were excluded from the study.Reference Zareifar, Farahmand Far, Golfeshan and Cohan28 Consequently, the difference in WBC levels between the patients and control subjects is not statistically significant. As the control subjects were age-matched with the patients, there was no statistically significant difference in age between the patients and the control subjects. We attempted to make the groups as homogeneous as possible in order to exclude variables other than tinnitus that may have affected mean platelet volume.
There are debates as to whether mean platelet volume has any association with inner-ear disorders. Sagit et al. found a positive relationship between mean platelet volume and sudden sensorineural hearing loss.Reference Sagit, Kavugudurmaz, Guler and Somdas29 Ulu et al. reported similar findings, with a positive relationship between mean platelet volume and sudden hearing loss.Reference Ulu, Ulu, Ahsen, Yucedag, Aycicek and Celik30 In contrast, Karli et al. and Bláha et al. found no correlation between mean platelet volume and sudden sensorineural hearing loss.Reference Karli, Alacam, Unal, Kucuk, Aksoy and Ayhan31, Reference Bláha, Košťál, Dršata, Chrobok, Lánská and Zák32 These papers have been discussed at length; the debate is ongoing, and there are advocates of both viewpoints.
• Many factors may lead to tinnitus, including otological, neurological, infectious, drug-related and physiological disorders
• The average size of platelets is referred to as mean platelet volume
• Bigger platelets result in more granules and better haemostasis
• Bigger platelets have been observed to be associated with tinnitus
According to the results of the current study, there is a positive relationship between mean platelet volume and tinnitus. The possible mechanism for the relationship is controversial. It is fairly clear that higher mean platelet volume is associated with a higher risk of atherosclerosis.Reference Ma, Lin, Hu, Li, He and Jin33–Reference Yüksel Kalkan, Gür, Baykan, Uçar, Elbasan and Şahin36 Higher mean platelet volume may play a role in thrombosis of the internal auditory artery and its branches, which may result in impaired perfusion of the inner ear and tinnitus. This theory would seem to be supported by the results of this study, but of course there are limitations to this study. The pathophysiological mechanism is unclear; mean platelet volume is affected by many parameters, and tinnitus severity may be a matter for discussion.
Conclusion
This study provides clinical evidence of higher mean platelet volume in tinnitus patients. However, there are some limitations, including the fact that tinnitus severity was not assessed. In addition, the pathophysiological mechanism of the relationship is unclear. Further studies are required for full clarification of these issues.
