To describe a case of bulbar-predominant myasthenia gravis (MG) that mimicked a structural brainstem lesion emphasizing clinical-radiological dissociation to prevent misdiagnosis.

Miastenia Gravis is an autoimmune disorder of the neuromuscular junction characterized by fluctuating weakness and muscle fatigability, with a classic ocular presentation. However, in some cases, bulbar involvement may predominate. The presence of incidental neuroimaging findings, such as brainstem lesions, can delay diagnosis and lead to misinterpretation. This scenario represents a diagnostic challenge, particularly in young patients with progressive symptoms.

A 23-year-old woman with autoimmune thyroiditis came in with a four-month history of worsening asymmetric ptosis, diplopia, dysphonia, and severe dysphagia. The examination showed diplegia facialis, palatal droop, an absent gag reflex, and lingual weakness (2/5) with fasciculations, as well as proximal limb fatigability and respiratory insufficiency (Single Breath Count (SBC): 3). A brain MRI showed a non-enhancing tectal cystic lesion that looked like a low-grade glioma at first. However, the absence of long-tract signs and the fact that symptoms changed over time pointed to a neuromuscular junction disorder. The presence of anti-AChR antibodies confirmed the diagnosis of generalised Myasthenia Gravis. Even though the patient was stable at first, a respiratory infection caused a crisis that needed ICU admission and intravenous immunoglobulin. After aggressive immunotherapy and corticosteroids, she achieved significant recovery (SBC >20). During follow-up, she experienced intermittent diplopia, demonstrating a favourable response to immunomodulatory treatment and a gradual decrease in corticosteroid dosage.

This case underscores the significant risk of misdiagnosis in bulbar-predominant MG, which can resemble brainstem structural lesions, particularly when incidental neuroimaging findings are present. Clinical-radiological dissociation, symptom variability, and fatigue are essential diagnostic indicators. Early diagnosis prevents unnecessary interventions and enhances outcomes through suitable immunomodulatory therapy. This case underscores the statement that “not all imaging findings elucidate the clinical presentation.”