Carbohydrate metabolism in hypothyroid myopathy

Area of Science:

• Endocrinology
• Metabolic Research
• Muscle Physiology

Background:

• Hypothyroidism is associated with metabolic disturbances.
• Carbohydrate metabolism alterations in hypothyroidism are not fully understood.
• Skeletal muscle dysfunction (myopathy) is a common complication of hypothyroidism.

Purpose of the Study:

• To investigate carbohydrate metabolism in hypothyroid patients.
• To identify potential metabolic defects contributing to hypothyroidism-induced myopathy.

Main Methods:

• Blood samples were collected after an overnight fast to measure glucose, lactate, alanine, and free fatty acids.
• Skeletal muscle biopsies were analyzed for glycogen content and acid maltase activity.
• Forearm ischemic stimulation was performed to assess lactate response.

Main Results:

• Untreated hypothyroid patients exhibited significantly lower blood glucose (24%) and lactate (35%) levels compared to treated patients and normal subjects.
• Skeletal muscle biopsies revealed normal glycogen content but reduced acid maltase activity in hypothyroid patients with myopathy.
• Hypothyroid patients showed an impaired lactate elevation in response to forearm ischemic stimulation.

Conclusions:

• Impaired glycogenolysis in skeletal muscle is a key finding in hypothyroid patients.
• Reduced acid maltase activity may underlie the impaired glycogenolysis.
• Impaired skeletal muscle glycogenolysis is a potential contributing factor to myopathy in hypothyroidism.