Strokes and amnesia were written off as anxiety. It was Hashimoto's encephalopathy.

A shadow of anxiety

A 56-year-old African American woman had a medical history that included nodular thyroid disease and anxiety. For her anxiety, she was prescribed 10 mg of Valium as needed. Prior to her current crisis, she had been hospitalized for double vision and weakness, which clinicians suspected was myasthenia gravis. She was treated with intravenous immunoglobulin (IVIG) and improved, despite testing negative for the associated antibodies.

The loss of consciousness

The woman was soon back in the hospital, this time presenting with an acute onset of decreased level of consciousness. On evaluation, she was somnolent and had 3/5 muscle strength in her right upper arm. Most strikingly, she was unable to recall any events from the past several weeks.

Initial imaging of her head and blood vessels appeared unremarkable. However, an MRI of her brain eventually revealed bilateral cortical and subcortical symmetric watershed strokes—a pattern often associated with a sudden drop in blood flow or blood pressure. Yet, there was no record of cardiac arrest or significant hypotension that could explain the damage.

Searching for the cause

Doctors performed a lumbar puncture, which showed 192 nucleated cells in her cerebrospinal fluid, 94% of which were lymphocytes. This indicated significant inflammation in the central nervous system. A wide net was cast: tests for infectious diseases like HIV and cryptoccolus were negative, as were panels for autoimmune and paraneoplastic conditions.

While her thyroid function tests showed a low TSH of 0.21 μIU/mL, it was her antibody levels that stood out. Her anti-thyroglobulin antibodies were 13.5 IU/mL and her anti-microsomal antibodies were 45.8 IU/mL, both significantly above the normal range. These markers, combined with her brain inflammation, pointed toward Hashimoto’s encephalopathy (HE).

The "stroke chameleon"

Hashimoto’s encephalopathy is sometimes called a "stroke chameleon." It is a rare condition where high levels of antithyroid antibodies are associated with cognitive decline, psychosis, and neurological deficits. In this case, clinicians hypothesized that the disease might have caused microvascular disruption, leading to blood pressure dysregulation and the symmetric strokes seen on her MRI.

Recovery through the fog

Because Hashimoto’s encephalopathy typically responds well to steroids, the patient was started on a five-day course of high-dose methylprednisolone. The treatment led to a clinical resolution of her mental status. Her right-side weakness and her amnesia showed partial improvement.

She was discharged with a steroid taper and scheduled for follow-up with neurology, endocrinology, and rheumatology. While her history of anxiety and vague weakness had initially framed her as a psychiatric or neuromuscular patient, the discovery of the thyroid antibodies revealed an autoimmune process that had been hiding in plain sight.