This patient should be treated with modafinil. She is experiencing fatigue related to her multiple sclerosis (MS). Fatigue is a very common symptom of MS but is often underevaluated and undertreated. Given this patient's decreased work performance and need for daytime sleep, pharmacologic treatment is indicated. The stimulant medications modafinil and armodafinil are frequently used in patients with MS. Amantadine also is an effective therapy for fatigue. For fatigue refractory to these medications, methylphenidate or other amphetamines may be considered.

Iron supplementation is an appropriate treatment for iron deficiency anemia, which can sometimes result in fatigue and always should be excluded as a cause in patients with MS. However, this patient's normal hemoglobin level and normal mean corpuscular volume argue against her being iron deficient.

Although hypothyroidism also can result in fatigue, this patient is clinically euthyroid, and her thyroid-stimulating hormone level is normal. Thyroid hormone supplementation in the absence of hypothyroidism is not appropriate treatment for the fatigue associated with MS.

Nocturnal continuous positive airway pressure (CPAP) can be an appropriate treatment of obstructive sleep apnea (OSA) and other causes of daytime sleepiness, such as primary sleep disorder. OSA should be considered in patients with MS and severe fatigue. However, this patient has no clinical history consistent with OSA, and thus prescribing CPAP without diagnostic polysomnography would not be appropriate.

This patient's history, physical examination, and imaging findings give no indication that her disease-modifying drug is resulting in treatment failure. Therefore, the teriflunomide does not have to be replaced with dimethyl fumarate or any other drug. In addition, fatigue is not a known adverse effect of teriflunomide, and this patient's fatigue is not a sign of medication intolerance.