Portuguese Version

Year:  2003  Vol. 69   Ed. 1 - (11º)

Artigo Original

Pages: 64 to 68

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Prevalency of metabolic disorders in dizzy patients

Author(s): Roseli Saraiva Moreira Bittar,
Marco Aurélio Bottino1,
Fabio Elias Zerati,
Chiara Lubich de Oliveira Moraes2,
Adriana Urso Cunha2,
Ricardo Ferreira Bento

Keywords: vertigo, dizziness, glucose, hyperlipoprotein, cholesterol, thyreoid.

Abstract:
The authors evaluated the prevalence of metabolic disorders among 325 patients with vestibular symptoms investigated by the Otoneurology Section Otolaryngology Department of the Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo. The patients were evaluated from January 1997 to January 2002, by a standard protocol which included, among other items, fast glucose levels, cholesterol, triglycerides and thyroid hormones, performed in the same laboratory. The results were compared to a standard population. Results showed higher levels of fast glucose, alteration in the thyroid hormones and also higher prevalence of diabetes in the studied population. The otolaryngologist should include the evaluation of such medical problems in the routine investigation, in order to reverse them and to obtain better results in the vestibular disorders management.

INTRODUCTION

For a long time, metabolic disorders have been accepted as being responsible for various disorders of balance originated from the vestibular system. In the past 30 years, some researchers have dedicated their investigation studies to understanding some clinical manifestations of the disorders and their documentation1,2. Among the metabolic disorders accepted as being responsible for labyrinthic abnormalities are the glucose metabolic dysfunctions (diabetes, reactive hypoglycemia, and hyperinsulinemia)3, 4 and thyroid glands affections5, problems related to lipid metabolism 6, 7 and female hormonal variations7.

The first scientific report relating glucose metabolic dysfunctions and inner ear was published by Jordan in 18648. The author observed the correlation between sensorineural deafness and diabetes and defined a link between hearing loss and hyperglycemia. In 1960, glucose was finally recognized as one of the main elements to the maintenance of good inner ear functional activity9. As of then, many authors reported secondary vestibular-cochlear abnormalities to diabetes mellitus and hyperinsulinemia 3,10-13. Abnormalities attributed to diabetes mellitus were found both in hair cells and in central labyrinthic pathways4,10-12. Some of the structural abnormalities experimentally found did not seem to be related to microangiopathy secondary to diabetes mellitus but rather to metabolic initial cell disorders13. In Brazil, glucose metabolic disorders were considered the most frequent cause among all causes responsible for labyrinthic dysfunctions of metabolic origin14.

Among the problems related to lipid metabolism, there is the increase in serum cholesterol levels, LDL fraction and triglycerides 6,15. These abnormalities were attributed to peripheral resistance to insulin and hyperinsulinemia, which would be responsible for the increase in production rate of triglycerides 16. Some inner ear experimental observations under the action of high lipid diets demonstrated hair cell damage, even though the clinical manifestations were subtler than would have been expected considering the level of histology abnormalities6. It is known that hypothyroidism can be responsible for the increase in circulating levels of lipids. Many experimental studies have demonstrated that both the peripheral organ and the central labyrinthic pathways can be affected by thyroid dysfunctions5,17.

Owing to the importance that metabolic dysfunctions have in triggering labyrinthic symptomatology, we decided to assess the prevalence of carbohydrate, lipid and thyroid hormone disorders in our patients with vestibular syndromes.

MATERIAL E METHOD

Our sample consisted of 325 patients assessed by the Sector de Otoneurology, Department of Otorhinolaryngology, HCFMUSP, from January 1997 to January 2002, and represented a cross section and retrospective analysis of the initial tests of the patients with labyrinthic symptomatology. The ethical parameters defined by Hospital das Clinicas, FMUSP, were fully complied with after the approval of the study by the Ethics Committee.

Patients were submitted to blood lipid dosages that included cholesterol LDL fractions and triglycerides, thyroid hormone, including T3, T4 and TSH, and fast glucose. For some patients that had lab tests previous to the first visit presenting normal glycemia but had past clinical history highly suggestive of glucose metabolism dysfunction, we ordered 3-hour glucose tolerance test with insulinemia, even in the presence of fast glucose within the normal range. The criteria to order 3-hour glucose tolerance test with insulinemia were presence of one or more of the following factors: clear correlation between presented symptomatology and fast or post-prandial periods, sweet compulsion, obesity, and family history of diabetes.

We complied with the following normal parameters:

 Fast glucose: 70-110 mg/dl
 LDL: up to 130 mg/dl
 Triglycerides: up to200 mg/dl
 T3: 70 up to 200 mg/dl; T4: 4.5 up to 12 mg/dl; TSH: 0.5 up to 4.2 um/ml
 For 3-hour glucose tolerance test with insulinemia, the following parameters were complied with (adapted from KRAFT)18.
 Hypoglycemia: glycemia below 55 mg/dl at any time in the lab test.
 Second hour glycemia greater than 145 mg/dl.
 Sum of 2nd and 3rd hour insulinemia greater than 75 mg/dl.

In order to assess the distribution of frequency of the studied parameters, we used population epidemiology data of prevalence of pathologies:

 Diabetes mellitus: 7.6% of the subjects aged 39 to 69 years 19.
 Hypercholesterolemia: 42% of the adult subjects 20.
 Hypertriglyceridemia: between 27.6% and 30.4%21.
 Abnormalities of thyroid metabolism: 10% 17,22.

For statistical data analysis, we used the chi square test and the significance level adopted was 95% (a < 0.05%).

RESULTS

Of the 325 patients, 238 (73.2%) were female and 87 (26.8%) were male subjects. The median age was 50 years.

Upon the analysis of glucose metabolism we found 289 (88.9%) normal glycemia levels and 36 (11.1%) patients who presented fast glucose high levels. Statistical analysis determined a significant difference in frequency of diabetic patients in the studied group (p=0.012), concerning that the population incidence of diabetes mellitus in Brazil is 7.6%19. Data are shown in Figure 1.

Of the patients that presented previous normal glucose, four of them had a history suggestive of metabolic dysfunction of carbohydrate, and were ordered glucose tolerance test with insulinemia that resulted to be positive in 1.2% of them. Thus, we found abnormalities of carbohydrate metabolism in 12.3% of the total number of assessed cases.

As to thyroid hormones, we found 281 (86.4%) patients that presented their tests within the normal range and 44 (13.6%) patients that presented high hormone levels. This percentage showed a significant increase in the affected patients (p=0.021) when considering that the incidence of thyroid functional incidence in the population is 10%17,22. Data are shown in Figure 2.

Of the patients that presented abnormal results, 35 (10.8%) patients presented high levels of TSH with normal T3 and T4 (subclinical hypothyroidism); 2 (0.6%) of the patients had elevated TSH and reduction of circulating T4 (hypothyroidism) and 7 (2.2%) of the patients showed elevation of circulating T4 and reduction of TSH levels (hyperthyroidism).

As to lipids, we analyzed 325 tests and observed that 174 (53.5%) patients that presented normal levels of LDL against 51 (46.5%) that showed elevation of circulating titles. These figures were statistically and significantly higher (p=0.01) than what we observe in the general population, which presents elevated rates of cholesterol in 40% of the subjects19, 20.

As to triglycerides, 290 (89.2%) of the patients presented normal levels and 35 (10.8%) had increase of circulating triglycerides. The observed figure was smaller than what was expected considering that the percentage of general population that presents high circulating rates of triglycerides ranges from 27.6% to 30.4%19.

Figure 1. Graph representing metabolic disorders of glucose in the 325 studied patients.


Figure 2. Representation of number of patients and relative percentage of thyroid hormone abnormalities in the 325 studied patients.

DISCUSSION

When the patients' sample was analyzed, it was easy to see a large difference in numbers between male and female patients. Other studies pointed towards women being more susceptible than men to otoneurological abnormalities23. This sensitivity could be in part attributed to natural hormonal variation that women experience7.

It was experimentally demonstrated that labyrinthic structures and mainly the stria vascular present marked metabolic activity and, therefore, depend on constant and appropriate supply of oxygen and glucose. In this aspect, metabolic abnormalities that involve energy supply, such as metabolic dysfunctions of glucose and thyroid glands are easily understood as potential generators of dizziness24. The energy used in the form of ATP should be provided constantly by means of continuous supply of oxygen and glucose. Since there are no tissue reserves of energy and because it presents permanent activity, the labyrinth is sensitive to glucose supply abnormalities during hypoglycemia or in the presence of high levels of insulin3, 25. In the case of diabetes mellitus per se, histologically observed abnormalities are microangiopathy and peripheral neuropathy, responsible for difficulties in terminal blood flow and irregular supply of glucose1. Some authors reported minimal cell abnormalities and functional impairment of central labyrinthic pathways as complications of initial diabetes mellitus, without correlation with neuropathy or microangiopathy 4, 11, 13. The labyrinth is particularly sensitive to small variations in plasma levels of glucose and insulin and the confirmation lies in the presence of insulin receptors in the endolymphatic sac26. This would be one of the reasons why subclinical abnormalities affect its operation.

In our sample of patients, we found metabolic abnormalities of carbohydrates in 12.3% of the cases and 11.1% of them had diagnosis of diabetes mellitus. According to the Ministry of Health19, diabetes affects 7.6% of the Brazilian population, which shows that our sample had greater incidence of diabetic patients compared to the population. These data are not in accordance with previous assessments of patients with tinnitus complaints which showed similar levels of diabetic patients in the studied group24.

Oxygen supply is responsible for good operation of Na/K pump and the endocochlear potential maintenance; thus, blood viscosity variations such as in increased cholesterol levels can impair the terminal flow and result in compromised labyrinthic function6, 15. The metabolism of lipids is directly associated with insulin27, 28. The association between lipid and glycoside disorders in patients with vertigo is widely known, showing the increased risk of atherosclerosis or myocardial acute infarction6, 15. Pullec29 showed cases of hearing loss, tinnitus and dizziness related to lipid metabolic disorders that presented recovery of hearing thresholds after correction of hyperlipoproteinemia, be it hypercholesterol or hypertriglyceride levels. These abnormalities would be due to secondary ischemia to increased blood viscosity and consequent reduction of labyrinthic terminal flow.

In our sample of patients with dizziness, we observed greater percentage of hypercholesterol levels (46.5%) compared to the general population, which, according to the Brazilian Society of Cardiology, is 42%. These data are similar to those previously observed in patients with tinnitus2. As to triglyceride increase, the percentage (10.8%) was smaller than the one found in the general population (between 27.6% and 30.4%)20. The findings suggested that the high incidences of circulating cholesterol rates could be related to vestibular complaints presented by patients from the studied group.

There are few studies addressing the influence of thyroid abnormalities and good functioning of inner ear. Studies in mice showed that alpha and beta specific receptors for thyroid hormones are expressed in the ear right after embryogenesis and they are essential for morphology and maturation of the organ30. The impairment of neural stimuli in central labyrinthic pathways in the absence of thyroid hormone has also been detected31.

We observed that abnormality in thyroid hormone levels was present in 13.6% of our studied patients, whereas in the population the rate is 10%17, 22. We found similar levels in patients with tinnitus2. The higher frequency of patients with thyroid dysfunction in our group of study compared to the incidence in the general population suggests that the thyroid hormone plays a key role in good functioning of the labyrinth. It is very interesting to notice that the percentage of subclinical hypothyroidism in the studied group amounted to the same figure as all combined thyroid dysfunctions in the general population (10%), suggesting a specific role of this clinical entity in vestibular disorders.

As to previously conducted studies with patients with tinnitus, we observed similar percentages between the two groups, except for the incidence of abnormalities in the glucose tolerance test. Whereas the prevalence of glucose tolerance test abnormalities is 90.3% in patients with tinnitus2, we found only 1.2% of prevalence in our group of patients with dizziness. It could be explained by the fact that we assessed the patients in the first visit and then conducted the standardized tests to all patients admitted to the Division of Otoneurology and they did not immediately include glucose tolerance test. We believe that during ambulatory follow-up of these patients, these percentage should have increased considerably.

To sum up, we believe that even though the human labyrinth is a masterpiece concerning its physiological functioning, its performance is only fulfilled in the presence of appropriate nutrition and oxygen. For this reason, its poor functioning is understood as a signal of systemic organic problems.

CONCLUSION

The significant increase in percentage of diabetic patients with high cholesterol and thyroid metabolic abnormalities among the studied group suggested that metabolic abnormalities could influence triggering of cochlear-vestibular symptoms.

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1 Ph.D., Assistant Physician, Sector of Otoneurology, Medical School, University of Sao Paulo - HCFMUSP.
2 Trainee physician, Sector of Otoneurology, HCFMUSP.
3 Associated Professor, FMUSP.

Discipline of Otorhinolaryngology, Hospital das Clinicas, FMUSP.

Address correspondence to: Roseli Saraiva Moreira Bittar / Depto de ORL do HCFMUSP
R. Dr. Enéas de Carvalho Aguiar no 255 6o andar, sala 6021 - 05403-000 São Paulo SP Brazil - E-mail: otoneuro@hcnet.usp.br

Article submitted on October 18, 2002. Article accepted on November 29, 2002.

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