Lyme patients have a higher prevalence of other autoimmune diseases. Generally with autoimmune disorders there is a genetic predisposition; but specific infections, Lyme included, may trip the autoimmune switch. One frequent, Lyme associated disorder is hypothyroidism. The diagnosis is frequently used interchangeably with Hashimoto's disease. The hallmark is the presence of the thyroid antibody TPO, thyroid peroxidase. Most physicians screen for hypothyroidism by checking TSH levels. I have found this to be inadequate. I also order thyroid antibodies whose presence may precede "chemical hypothyroidism." Symptoms may occur despite normal TSH levels. There is debate about what is the optimal TSH. I believe the optimal TSH level is less than 2 rather than the conventional 4. Patients are confused because higher levels correspond to lower thyroid levels and lower number correspond to higher thyroid levels. TSH does not measure thyroid levels. It measures a pituitary hormone which stimulates the output of thyroid hormone. It is a much more sensitive marker than the direct measurement of the thyroid hormones, T3 and T4. In other words, the TSH is inversely related to thyroid level.
Traditionally, thyroid supplementation is with T4 only products like Synthroid. T4 is inactive and converted to T3, the active hormone, peripherally, in blood and organs. I believe the solo T4 therapy is frequently be sub-optimal. Since the thyroid gland secretes both T3 and T4 combination therapy with the two more closely simulates normal physiology. Armour thyroid is a combination product derived from desiccated pig hormone may be used. Alternatively, synthetic T4 and T3 can be combined. T3 is commercially available as Cytomel. T3 is 4 times more potent than T4 so the two should not be taken in equal proportion. T3 appears to be more energizing and perhaps more active in the brain and central nervous system. T3 supplementation is problematic because of its short half life. The dose may be divided into small fragments taken at least twice daily. Another option is to have T3 compounded into a slow release capsule.
Thyroid supplementation is sometimes used even when a patient is "euthyroid" with normal thyroid levels. Depression is a common feature shared by many Lyme sufferers. T3 has long been known to work as an antidepressant booster when combined with other antidepressants.