ELSEVIERArchives of Gerontology and Geriatrics

33 (2001) 295-300

ARCHIVES OFGERONTOLOGYAND GERIATRICS

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Subclinical thyroid disease in patients withParkinson's disease

Howard Tandeter a,*, Amalia Levy b, Guy Gutman c,Pesach Shvartzman a

" Department of Family Medicine, Healtll Sciences Faculty, Ben-Curion University of the Negev,PO Box 653, Beer-Sheva 84/05. Israel

b Department of Epidemiology, Health Sciences Faculty, Ben-Curhlll University of the Negev,PO Box 653, Beer-Sheva 84105, Israel

CDepartment of Pediatrics 'A', Schneider Hospital, Petach-Tikva, Israel

Received 2 March 2001; received in revised form 16 July 2001; accepted 19 July 2001

Abstract

The objective of this study was to determine whether hypothyroidism is more common inParkinson patients than in a control group without Parkinson, as suggested in the past. Weperformed a retrospective file review of all admissions to the geriatric ward during a I-yearperiod. Concentrations of thyroid stimulating hormone (TSH) and thyroxine (T4) from 92Parkinson patients were compared with those of 225 randomly selected controls from thesame ward. Hypothyroidism was not found to be more common in patients with Parkinsondisease as previously suggested. Incidentally, we found an unexpected increase in theprevalence of abnormal thyroid laboratory tests in this group. Statistically significantdifferences were found in two subgroups, (1) men with Parkinson were more likely to haveabnormal thyroid laboratory tests as compared with controls; and (2) 'subclinical' hyperthy-roidism was found to be more prevalent in Parkinson patients than in controls. Furtherresearch in this field is warranted in non-hospitalized patients. <Q2001 Elsevier ScienceIreland Ltd. All rights reserved.

KcY'I!orcll-: Parkinson disease; Thyroid stimulating hormone; Hypothyroidism

* Corresponding author. Tel.: + 972-8-6477-436; [ax: + 972-8-6477-636.

E-mail address: howard@bgumail.bgu.ac.il (H. Tandeter).

0167-4943/01/$ - see front matter «d 2001 Elsevier Science Ireland Ltd. All rights reserved.

PH: SOI67-4943(01)00196-0

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296 H. T{//u/e/er e/ al. / Arch. CC/'ol1/ol. Ceria/r. 33 (2001) 295-300

1. Introduction

Parkinson's disease (PO) is a common disorder, with an overall prevalence risingfrom 0.6'Yoat age 65-69 up to 3.5'Yoat age 85-89 (Oe-Rijk et aI., 1997). Whenhypothyroidism develops in these patients, the diagnosis may be overlooked, assome of the classic clinical manifestations of the two disorders are similar (Bergerand Kelley, 1981; Johannessen et aI., 1987; Tandeter and Shvartzman, 1993), unlessthyroid function tests are routinely done. In the past some researchers have founda high prevalence of hypothyroidism among PO patients (Berger and Kelley, 1981),but others could not confirm this (Johannessen et aI., 1987). The present study wasdesigned to define whether hypothyroidism is indeed more common in patients withPO than in those without PO. We report some unexpected results.

2. Patients and methods

We reviewed the files of all patients admitted to the geriatric ward of the SorokaUniversity Medical Center, in Israel, between 1995 and 1996. We identified 92patients with PO (62% male and 38% female). From the same chart review werandomly selected a control group of 225 patients (34% male, and 66% fen1.ale),who did not have a diagnosis of PO. The mean age of the patients was similar inthe study group and the control group (78.78 vs. 78.33). Concentrations of thyroidstimulating hormone (TSH) and free thyroxine (T4), routinely performed on allpatients on admission to this ward, were measured by standardradioimmunoassays.

For the contingency table analysis, the X2 or Fisher's exact test were used, asappropriate and P:::;:0.05 was considered significant.

3. Results

"

Hypothyroidism was not found to be significantly more prevalent in PO patients.Patients were classified as having normal or abnormal thyroid laboratory tests.

Abnormalities in thyroid tests were classified as.I. Hypothyroidism, (high TSH and Iow T4).2. Hyperthyroidism, (Iow TSH and high T4).3. Subclinical hypothyroidism, (high TSH with normal T4).4. Subclinical hyperthyroidism, (Iow TSH with normal T4).

Overall, 25'Y"of the subjects in our study group had some abnormality in theirthyroid laboratory tests as compared with 16'1"0in the control group (Table I). ThisdilTerencewas found to be statistically borderline significant (P = 0.06). When menclOdwomen were analyzed separately, we found that 22.8% of the male populationin the study group had some abnormality in their thyroid laboratory tests ascompared with 10.3% of the controls. This difference did show to be statisticallylignificant (P < 0.05).

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Table I

Thyroid laboratory tests

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N-.0......

Study group Control group P value

Male (n=57) Female (n = 35) Total (n = 92) Male (n = 77) Female (n = 148) Total (n = 225)

n % n % n % n % n % n %

Normal thyroid laboratory tests 44 48 25 27 69 75 69 31 120 53 189 84

Abnormal thyroid laboratory tests 13 22.8 10 28.5 23 25 8 10.3 28 18.9 36 16 0.06

High TSH normal T4 6 10.5 6 17.1 12 13 5 6.5 22 14.8 27 12 NS

High TSH Iow T4 2 3.5 0 0 2 2.1 I \.3 2 \.3 3 \.3 NSLow TSH normal T4 3 5.2 4 11.4 7 7.6 2 2.6 4 2.6 6 2.3 P<O.O

Low TSH high T4 2 3.5 0 0 2 2.1 0 0 0 0 0 0 NS

Comparison between PO patients and controls without PD.

298 H. Tandeler el al. / Arch. Ceronlol. Cerialr. 33 (200/) 295-300

Subclinical hyperthyroidism was found to be significantly more prevalent (P <0.05). in Parkinson patients as compared with the control group (Table 1).

4. Discussion

The intention of this study was to test whether hypothyroidism is more commonin patients with PD than in the general population. The search was motivated bythe conflicting results presented in two previous studies (Berger and Kelley, 1981;Johannessen et aI., 1987). Our findings did not confirm that hypothyroidism is morecommon in PD patients but unexpectedly showed that men with PO, had morethyroid laboratory tests abnormalities than controls, and that 'subclinical hyperthy-roidism' was more prevalent in patients with PD than in controls. Subclinicalhypothyroidism/hyperthyroidism are incidental findings in asymptomatic patients.Thirty-four percent of patients with subclinical hypothyroidism may develop overthypothyroidism in a la-year follow-up (Huber et al., 1998), and the presence ofthyroid antibodies increases the risk of developing overt hypothyroidism (Weetman,1997). In subclinical hyperthyroidism, the incidence of progression to overt thyro-toxicosis is nearly 5% per year (Wiersinga, 1995). Reported unwanted effects ofsubclinical hypothyroidism include memory impairment (Monzani et al., 1993;Baldini et aI., 1997), depression (Haggerty et aI., 1993); elevated low densitylipoprotein (LDL)-cholesterol levels and Iow high density lipoprotein (HDL)-cholesterol levels (Kung et al., 1995; Bindels et aI., 1999) [thyroid substitutiontherapy may decrease total cholesterol (Tanis et al., 1996)]; impaired muscle energymetabolism (Monzani et al., 1997); and impaired diastolic function (Biondi et aI.,1999). Reported pathology associated with subclinical hyperthyroidism includes aslightly increased bone turnover that may lead to a reduced bone mass anddecreased bone density (Faber et al., 1998); atrial fibrillation (Koutras, 1995); andpossible increase in left ventricular systolic function and mass, impaired diastolicfunction, reduced maximal exercise capacity, reduced ejection fraction duringexercise (Hanna et al., 1999). However, despite a possible association between'sub-clinical' disease and pathology, there is no universal recommendation for thetreatment of these entities, and screening programs are not recommended since theassociated burden of disease is small and early diagnosis and treatment has notbeen shown to improve clinical outcome in the asymptomatic phase.

One hypothesis about a likely 'relation' between PD and thyroid disorderssuggests a possible role of iodine deficiency in PD and Alzheimer's disease, as inhypothyroidism (Foster, 1987). Another possible mechanism relating thyroid dis-ease and PD may be a disturbance in pituitary hormone secretion due to hypotha-lamic dysfunction (Otake et al., 1994).

We recognize some limitations in our data. The number of subjects studied isrelatively small. Testing hospitalized patients was convenient but not ideal. Futureresearch in this field should be performed in the ambulatory setting, since hospital-ized patients may have a higher frequency of abnormal thyroid function tests thanasymptomatic ambulatory elderly (Cervantes-Covarrubias et al., 1992) and do not

fI. Tal/deler el al. / Arch. GerOl/lol. Gerialr. 33 (200I) 295-300 299

necessary reflect the characteristics of the general population. In conclusion, an'unexpected increase in the prevalence of some abnormal thyroid laboratory testswas found in a cohort of hospitalized PD patients as compared with a controlgroup. Further research in this field is warranted, in order to clarify the details,since there are implications both for the understanding of the basic mechanismsthat might link the two disorders, and for clinical practice.

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