Differential Diagnosis for Hypothyroid Patient with New Symptoms after Starting Levothyroxine

Single Most Likely Diagnosis

• Levothyroxine-induced hyperthyroidism or too rapid correction of hypothyroidism: This is the most likely diagnosis because starting levothyroxine, especially if the dose is too high or the increase is too rapid, can lead to symptoms of hyperthyroidism, including dizziness, vertigo, and headache, as the body adjusts to the new thyroid hormone levels.

Other Likely Diagnoses

• Meniere's disease or other inner ear disorders: These conditions can cause vertigo and dizziness and may be exacerbated or uncovered by the initiation of thyroid hormone replacement, although they are not directly caused by levothyroxine.
• Migraines: Some patients with hypothyroidism may experience migraines, and the initiation of thyroid hormone replacement could potentially affect migraine frequency or severity, leading to headaches and possibly vertigo.
• Anxiety or panic disorder: The onset of treatment and the body's adjustment to new hormone levels might exacerbate or trigger anxiety or panic disorders, which can present with dizziness, vertigo, and headaches.

Do Not Miss Diagnoses

• Cerebrovascular accident (CVA) or transient ischemic attack (TIA): Although less likely, it is crucial not to miss a CVA or TIA, as these conditions are medical emergencies. The sudden onset of dizziness, vertigo, and headache could be indicative of a stroke, especially in patients with risk factors.
• Pituitary apoplexy: This is a rare but potentially life-threatening condition that could occur in the context of pituitary disorders leading to hypothyroidism. The initiation of levothyroxine might not directly cause apoplexy, but any acute change in pituitary function could potentially precipitate this condition.

Rare Diagnoses

• Autoimmune disorders: Certain autoimmune disorders, such as Hashimoto's encephalopathy, could potentially cause neurological symptoms including dizziness, vertigo, and headache. However, these are rare and would typically be associated with other systemic or neurological symptoms.
• Thyroid storm: Although extremely rare as an initial presentation after starting levothyroxine, a thyroid storm is a life-threatening condition that requires immediate recognition and treatment. It is more commonly associated with untreated or undertreated hyperthyroidism but could theoretically occur in the context of too rapid correction of hypothyroidism.