[Note: Though many physicians believe individuals with thyroid stimulating hormone levels of 5 to 25 don’t have symptoms of hypothyroidism, others believe this ‘subclinical’ hypothyroidism is often associated with nerve and muscle problems.]
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. [The strength of the inspiratory muscles used to inhale – the diaphragm and muscles that lift the rib cage to take air in – is considered a crucial measure in those with neuromuscular disorders.] 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 manual muscle testing were significantly more frequent in subclinical hypothyroidism than in controls, and inspiratory muscle strength was lower in patients with these abnormalities.
Results suggest that altered muscle strength by manual muscle testing and the coexistence of neuromuscular complaints in patients with subclinical hypothyroidism may indicate neuromuscular dysfunction.
Source: American Journal of the Medical Sciences, Sep 1, 2009. PMID: 19726974, by Reuters VS, de Fatima S Teixeira P, Vigario PS, Almeida CP, Buescu A, Ferreira MM, de Castro CL, Gold J, Vaisman M. Divisions of Endocrinology and Physical Medicine & Rehabilitation, Department of Internal Medicine; Department of Internal Medicine; Department of Cardiology, University Federal of Rio de Janeiro, Brazil.