What happened, in summary

A previously healthy woman in her mid-40s came to the emergency department with sudden anterograde amnesia, meaning she could no longer reliably form new memories. About 20 days earlier she had tested positive for COVID-19 and had mild respiratory symptoms, fatigue, and tiredness. Over the next 2 weeks, she developed vivid unfamiliar dreams, short-term memory loss, insomnia, and brief episodes of disorientation, crying, and intense anxiety that resembled panic attacks. On admission, she was disoriented in time and space, but the rest of her neurological examination was largely normal. She had no breast symptoms, no palpable lymph nodes, and no unexplained weight loss or night sweats. Her family history was notable: her mother had been treated for breast cancer in her 40s, and her maternal grandmother had breast cancer around age 65. During the workup, doctors diagnosed LGI1 antibody-positive limbic encephalitis, an immune-mediated inflammation affecting memory and seizures. Treatment began with intravenous immunoglobulins and antibiotics. When improvement plateaued, she received high-dose intravenous methylprednisolone, followed by rituximab given as 2 infusions 2 weeks apart. Her neurologic symptoms gradually improved. The same diagnostic evaluation also uncovered an asymptomatic early-stage breast cancer. Pathology described an infiltrative mixed carcinoma, predominantly no-special-type/ductal with a lobular component, grade I, measuring about 30 mm. The tumor was strongly hormone receptor-positive, with ER 95-100%, PR 80%, and HER2-negative status. After stabilization from encephalitis, the breast tumor was removed surgically. The breast cancer itself was not described as symptomatic. By 12 months after discharge, she had continued neurologic recovery and had returned to part-time work.