Hypo

By Peter Galvin, MD

Today’s case study comes from a teaching hospital in Sri Lanka. The 35-year-old man in Panel A presented to the medical ward with a two-year history of progressive weakness in his arms and legs associated with intermittent muscle cramping. He also had fatigue, weight gain, and constipation. Despite his symptoms, he had been able to continue working as a cattle herder. His vital signs were normal (blood pressure, heart rate, etc.). On physical examination he appeared fatigued. Macroglossia (enlarged tongue) and enlargement of the calves of his legs (Panel B) were noted, but no muscle enlargement of the arms was observed. He had proximal muscle weakness in the arms and legs and decreased deep-tendon reflexes (DTRs) with delayed relaxation (normally, DTRs have an equal flexion and relaxation time. When the relaxation time is prolonged, this is known as “hung-up” reflexes and is often seen in hypothyroidism). He had a history of Hashimoto’s thyroiditis, a disease that causes hyperthyroidism.

Lab testing showed a considerably elevated thyrotropin (TSH, or thyroid stimulating hormone) with low levels of both thyroid hormones – free thyroxine and triiodothyronine. (Like most endocrine systems, regulation of thyroid hormone levels uses a feedback system. When the pituitary gland in the brain detects a low level of thyroid hormone, it secretes more TSH in order to stimulate the thyroid gland to make more hormone). Also markedly elevated was the muscle protein creatine kinase (CPK). The level was 7087 (reference range 55 to 170). CPK rises in response to muscle injury. Thyroid peroxidase antibody levels were also markedly elevated. A diagnosis of Hoffman’s syndrome was made. This is hypothyroid myopathy with muscle pseudohypertrophy due to Hashimoto’s disease. Hashimoto’s causes hyperthyroidism which over time often cause the thyroid gland to “burn out,” causing hypothyroidism. The muscle enlargement, or pseudohypertrophy, in hypothyroidism is caused by the accumulation of glycosaminoglycans in muscle tissue. These are mucopolysaccharides, or complex sugars, that accumulate due to enzyme deficiencies in the muscles.

The patient was started on levothyroxine, or thyroid hormone replacement therapy. Three months later his symptoms had resolved, however the muscle enlargement persisted.

Please direct questions or comments to editor@rockawaytimes.com