Myasthenia Gravis Presenting With Vocal Cord Paralysis As the Initial Symptom Occurring One Week Following Herpes Zoster Vaccination: A Case Report and Review of the Literature

Myasthenia gravis (MG) is an autoimmune neuromuscular junction disorder primarily characterized by fluctuating skeletal muscle weakness. While it typically presents with ocular or generalized symptoms, vocal cord paralysis (VCP) as an initial manifestation is exceedingly rare and often leads to diagnostic delays. We report the case of an 86-year-old Japanese woman who developed progressive hoarseness, dysphagia, and respiratory distress approximately one week after receiving the inactivated herpes zoster vaccine (Shingrix®). Initial evaluation revealed unilateral VCP, which progressed to bilateral paralysis, requiring emergency intubation and subsequent tracheostomy. Despite extensive imaging and laboratory investigations, the etiology remained unclear until the patient developed diplopia and ptosis around hospital day 25. Although both anti-acetylcholine receptor (AChR) and anti-muscle-specific kinase (MuSK) antibodies were negative, the diagnosis of MG was confirmed through positive edrophonium and ice pack tests. Treatment included pyridostigmine, plasma exchange, and immunosuppressive therapy with tacrolimus and prednisolone. While ptosis improved, bilateral VCP and diplopia persisted at one year, and the patient remained tracheostomy-dependent but functionally independent. This case adds to the limited literature on laryngeal-type MG, a focal subtype marked by bulbar symptoms and often negative for AChR antibodies. Our review of post-2000 literature identified 13 cases of MG with VCP, 10 of which presented with VCP initially. Notably, nine required airway management, underscoring the potential for rapid respiratory compromise. This is the first reported case of MG development temporally associated with herpes zoster vaccination. Although a definitive causal link cannot be established, the close temporal sequence - fever and systemic immune activation shortly after vaccination, followed by MG onset - raises the possibility of an immune-mediated trigger. Previous reports have described MG onset after various other vaccines, including HPV, HBV, influenza, and COVID-19, suggesting that vaccination may rarely unmask or precipitate MG in susceptible individuals. Nonetheless, large-scale studies have not demonstrated a significant increase in autoimmune disease following vaccination, supporting the overall safety of immunization programs. This case highlights the importance of recognizing atypical MG presentations such as isolated VCP, particularly in the context of recent immune stimulation. Early diagnosis and appropriate treatment are critical for improving outcomes and preventing life-threatening complications such as airway obstruction. Heightened clinical suspicion is warranted in similar scenarios to facilitate timely intervention.