Overview

Migraine disorder is a common neurological condition affecting millions worldwide, while subclinical hypothyroidism is a mild thyroid disorder that often goes undetected. Recent research published in BMC Neurology reveals an important connection between these two conditions and suggests that treating subclinical hypothyroidism may help reduce migraine frequency and severity.

Understanding Subclinical Hypothyroidism

Epidemiology

In the United States NHANES III survey, 4.3% of 16,533 people had subclinical hypothyroidism (excluding those with known thyroid disease). The prevalence rises with age, is higher in females than males, and is lower in Black persons than in White persons. The prevalence may be lower than previously thought when using age-specific TSH reference ranges, as TSH normally rises with age.

Etiology (Causes)

The causes of subclinical hypothyroidism are the same as those of overt hypothyroidism:

• Chronic autoimmune (Hashimoto's) thyroiditis - most common cause
• Persistent TSH increase following thyroiditis (subacute, postpartum, painless)
• Thyroid injury (partial thyroidectomy, radioactive iodine therapy, radiation)
• Medications (iodine-containing drugs, lithium, interferon alfa, etc.)
• Inadequate replacement therapy for overt hypothyroidism
• Thyroid infiltration (amyloidosis, sarcoidosis, etc.)

The thyroid system works like a thermostat: when thyroid hormone levels drop, the pituitary gland increases TSH production to stimulate the thyroid. In subclinical hypothyroidism, the pituitary is working harder (producing more TSH) to maintain normal thyroid hormone levels, indicating early thyroid dysfunction.

Clinical Findings

Most patients with subclinical hypothyroidism have serum TSH levels less than 10 mU/L and are asymptomatic. Some patients may have vague, nonspecific symptoms suggestive of hypothyroidism, such as fatigue and constipation, but attempts to identify patients clinically have not been successful.

Older patients (over 65) with subclinical hypothyroidism appear to be particularly asymptomatic, although many euthyroid older individuals also have symptoms that might be construed as being related to hypothyroidism (dry skin, constipation, low energy).

Consequences of Untreated Subclinical Hypothyroidism

• Progression to overt hypothyroidism: 2-4% annual rate (33-55% over 10-20 years)
• Cardiovascular disease: Possible increased risk, particularly with TSH >10 mU/L
• Lipid abnormalities: Possible mild cholesterol elevations
• Reproductive abnormalities: Potential association with infertility
• Metabolic dysfunction–associated steatotic liver disease (MASLD): Higher prevalence of steatohepatitis and fibrosis
• Neuropsychiatric symptoms: Mixed evidence for association with depression and cognitive dysfunction
• Migraine: Increased frequency and severity of migraine headaches

The Migraine-Thyroid Connection

The relationship between migraine and subclinical hypothyroidism has been gaining attention in recent years. This systematic review and meta-analysis examined four studies involving over 322,000 participants to better understand this connection.

"Treatment with levothyroxine significantly decreased headache frequency and severity compared to the placebo group at three months of follow-up. Additionally, the treatment significantly decreased the MIDAS score, indicating a significant improvement in headache management."

Treatment Benefits

The research suggests that treating subclinical hypothyroidism with low-dose levothyroxine may help reduce migraine symptoms. In one randomized controlled trial, patients received 25 mg of levothyroxine supplementation for three months.

Treatment Recommendations Based on TSH Level

Arguments For and Against Treatment

Age is an important consideration when deciding on treatment. In older adults (>65-70 years), the upper limit of normal TSH may naturally be higher (6-8 mU/L), and treatment has shown less benefit. In contrast, younger patients, especially those with higher TSH values or migraine disease, may benefit more from treatment.

What This Means For You

If you have migraine, especially chronic migraine, these findings may have important implications for your care:

"The study highlights the importance of thyroid screening in migraine management, due to the link between hypothyroidism and migraines. It recommends routine thyroid function assessments for migraine patients and suggests personalized treatment approaches. Early intervention can minimize migraine episodes and improve quality of life."

Monitoring

For patients with subclinical hypothyroidism who do not receive thyroid hormone replacement, thyroid function tests (TSH, free T4) should be repeated initially at six months and, if stable, yearly thereafter.

For those receiving levothyroxine treatment, the goal is to reduce the TSH concentration into the normal reference range. For younger patients, a target TSH of 0.5 to 2.5 mU/L is often recommended. For older patients (≥65-70 years), a target TSH of 3 to 6 mU/L is more appropriate to avoid overtreatment.

Future Research

While the findings are promising, the researchers emphasize that more studies are needed to fully understand the relationship between subclinical hypothyroidism and migraine. Future research should focus on: