Clinical Investigation
Functional Capacity and Muscular Abnormalities in Subclinical Hypothyroidism

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Abstract

Background

Neuromuscular abnormalities and low exercise tolerance are frequently observed in overt hypothyroidism, but it remains controversial if they can also occur in subclinical hypothyroidism (sHT). The aim of this study is to evaluate neuromuscular symptoms, muscle strength, and exercise capacity in sHT, compared with healthy euthyroid individuals.

Methods

A cross-sectional study was performed with 44 sHT and 24 euthyroid outpatients from a university hospital. Neuromuscular symptoms were questioned. Muscle strength was tested for neck, shoulder, arm, and hip muscle groups, using manual muscle testing (MMT). Quadriceps muscle strength was tested with a chair dynamometer and inspiratory muscle strength (IS) by a manuvacuometer. Functional capacity was estimated based on the peak of oxygen uptake (mL/kg/min), using the Bruce treadmill protocol.

Results

Cramps (54.8% versus 25.0%; P < 0.05), weakness (45.2% versus 12.6; P < 0.05), myalgia (47.6% versus 25.0%; P = 0.07), and altered MMT (30.8% versus 8.3%; P = 0.040) were more frequent in sHT. Quadriceps strength and IS were not impaired in sHT and the same was observed for functional capacity. IS was significantly lower in patients complaining of fatigue and weakness (P < 0.05) and tended to be lower in those with altered MMT (P = 0.090).

Conclusion

Neuromuscular complaints and altered MMT were significantly more frequent in sHT than in controls, and IS was lower in patients with these abnormalities. Results suggest that altered muscle strength by MMT and the coexistence of neuromuscular complaints in patients with sHT may indicate neuromuscular dysfunction.

Section snippets

Study Design

A cross-sectional case-control study was performed, in which the presence of neuromuscular symptoms, muscle strength, and functional capacity of patients with sHT were investigated and compared with healthy subjects without thyroid diseases.

Patients

Individuals with sHT, defined as having elevated serum TSH (> 4.0 μUI/mL) and normal FT4 levels (0.9–1.8 ng/dL), were recruited from the outpatient clinic of Clementino Fraga Filho University Hospital in Rio de Janeiro, Brazil. Forty-four patients aged between

RESULTS

General characteristics of patients and controls are presented in Table 1. A higher prevalence of smokers was observed in the control group, but this did not interfere in the analyses [Figure 1, Figure 2]. Mean serum FT4 levels were statistically lower in patients than in controls (1.06 ± 0.19 versus 1.21 ± 0.16; P < 0.05), although all were in the reference range. As expected, TSH levels were markedly higher in sHT (5.1 ± 3.3 versus 1.4 ± 0.7; P < 0.05) (Table 1).

Complaints of cramps (54.8% versus 25.0%; P

DISCUSSION

Only a few studies have been published about neuromuscular alterations in sHT. In the current study, patients had a greater frequency of neuromuscular complaints than controls. They also had greater frequency of reduced muscle strength as evaluated by MMT in sHT than in controls, and this correlated positively with neuromuscular complaints. In addition, patients with altered MMT had lower median values of IS and QS. The frequency of abnormal QS was not different when comparing sHT and controls

CONCLUSIONS

Functional capacity was not apparently affected by sHT in the studied population.

Neuromuscular complaints and altered MMT were significantly more frequent in patients with sHT. Despite no difference being observed for QS and IS, they tended to be lower in patients with altered MMT and in those with neuromuscular symptoms. We believe that these findings may suggest a mild incipient neuromyopathy that must be considered in the decision to begin levothyroxine treatment.

Finally, we believe that

REFERENCES (28)

  • A.R. Ayala et al.

    Minimally symptomatic (subclinical) hypothyroidism

    Endocrinologist

    (1997)
  • K.A. Woeber

    Subclinical thyroid dysfunction

    Arch Intern Med

    (1997)
  • A.E. Hak et al.

    Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study

    Ann Intern Med

    (2000)
  • B. Biondi et al.

    Effects of subclinical thyroid dysfunction on the heart

    Ann Intern Med

    (2002)
  • G.J. Kahaly

    Cardiovascular and atherogenic aspects of subclinical hypothyroidism

    Thyroid

    (2000)
  • D.S. Cooper

    Subclinical hypothyroidism

    N Eng J Med

    (2001)
  • F. Monzani et al.

    Subclinical hypothyroidism: neurobehavioral features and beneficial effect of l-thyroxine treatment

    Clin Invest

    (1993)
  • M. Cakir et al.

    Musculoskeletal manifestation in patients with thyroid disease

    Clin Endocrinol

    (2003)
  • D.S. Cooper et al.

    l-Thyroxine therapy in subclinical hypothyroidism: a double-blind, placebo-controlled trial

    Ann Intern Med

    (1984)
  • F. Monzani et al.

    Clinical and biochemical features of muscle dysfunction in subclinical hypothyroidism

    J Clin Endocrinol Metab

    (1997)
  • R.F. Duyff et al.

    Neuromuscular findings in thyroid dysfunction: a prospective clinical and electrodiagnostic study

    J Neurol Neurosurg Psychiatry

    (2000)
  • A. Misiunas et al.

    Peripheral neuropathy in subclinical hypothyroidism

    Thyroid

    (1995)
  • N. Caraccio et al.

    Muscle metabolism and exercise tolerance in subclinical hypothyroidism: a controlled trial of levothyroxine

    J Clin Endocrinol Metab

    (2005)
  • E.A. Palmieri et al.

    Subclinical hypothyroidism and cardiovascular risk: a reason to treat?

    Treat Endocrinol

    (2004)
  • View full text