No Thyroid Problems With DMF Therapy, Records Study Concludes

Treatment with the approved multiple sclerosis (MS) therapy dimethyl fumarate (DMF) did not affect the function of the thyroid gland, an organ that secretes hormones to regulate metabolism, a medical records study concluded.

Screening for thyroid problems is not needed for people with MS considered for DMF therapy, the researchers recommended.

The study, “Thyroid Disorders in Patients Treated with Dimethyl Fumarate for Multiple Sclerosis: A Retrospective Observational Study,” was published in Antioxidants.

In MS, an abnormal immune attack against the brain and spinal cord causes lesions that lead to disease symptoms including fatigue, walking difficulties, numbness and tingling, muscle spasms or stiffness, vision problems, or bowel or bladder problems.

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DMF, sold as Tecfidera and under several generic forms, is an approved oral therapy for MS that helps slow the development of brain lesions and delay disability progression. DMF’s mechanism of action is still unclear, but it’s thought to modulate the immune system and stimulate neuroprotective pathways.

The thyroid is a butterfly-shaped gland located at the base of the throat that secretes hormones to control metabolism, the way body uses energy.

A 2019 report described the case of a 59-year-old woman with MS who developed abnormally low thyroid hormone levels, or hypothyroidism, two months after starting treatment with DMF, which was normalized soon after stopping the therapy. Before DMF, her thyroid function was normal despite having Hashimoto’s thyroiditis — an autoimmune disease characterized by an immune attack on the thyroid gland that triggers hypothyroidism.

This finding prompted researchers at the Lausanne University Hospital, Switzerland, to examine the medical records of 163 DMF-treated MS patients to assess the occurrence of thyroid disorders among this patient group.

Most participants (91.5%) had at least one thyroid-stimulating hormone (TSH) test to measure thyroid function; the majority (67%) had at least one TSH test before DMF, and more than one-third during DMF treatment (37%).

More than half were no longer under DMF treatment (54%), and of these, 40% had at least one TSH reading after DMF discontinuation, and about one-fifth (18.0%) had at least one TSH value recorded across all periods (before, during treatment, and after treatment  was discontinued).

Seven out of the 163 MS patients (4.3%) analyzed were diagnosed with a functional thyroid disorder. Among these, five were diagnosed before DMT treatment, with no evidence of thyroid disorder aggravation during or after DMF.

Functional thyroid disorder was diagnosed during or after DMF treatment in two patients (1.2%), one of whom developed mild hypothyroidism during treatment, which spontaneously normalized.

The other person developed hyperthyroidism, which is marked by too much thyroid hormone — after stopping 3.5 years of DMF treatment due to persistently low white blood cell counts. He was eventually diagnosed with Graves’ disease, an autoimmune disorder that causes hyperthyroidism.

Thyroid disorder due to abnormal growths on the gland occurred in five of the 163 DMF-treated MS patients (3%), but none of these developed during or after DMF treatment.

“The present study suggests that DMF probably has no direct toxic effect on the thyroid, as evidenced by a very low incidence of functional [thyroid disorder],” the researchers concluded. “However, it cannot be excluded that in rare instances it might induce [autoimmune thyroiditis] in susceptible patients with or without known preexisting [thyroid disorder].”

“The overall good thyroid tolerance of DMF indicates that specific screening for [thyroid disorder] is not required in MS patients considered for or treated with DMF,” the researchers said.