Unusual Presentation of Double-seronegative Myasthenia Gravis with Positive Anti-LRP4 Antibody: Diagnostic Utility of a Videofluoroscopic Swallowing Study

Abstract

An 86-year-old woman was admitted to our hospital with cryptogenic progressive dyspnea and dysphagia following a tracheostomy procedure 4 months prior to presentation. She exhibited fluctuating diplopia, bilateral vocal fold paralysis, normal nerve test results, negative findings for serum anti-acetylcholine receptor and anti-muscle-specific kinase antibodies, and positive findings for anti-LDL receptor-related protein 4 (LRP4). A videofluoroscopic swallowing study (VFSS) with edrophonium revealed an improvement in bulbar paralysis. Consequently, the patient was diagnosed with double-seronegative myasthenia gravis (DSN-MG) and began immunomodulatory therapy. This case emphasizes the diagnostic challenges of bulbar-type DSN-MG and underscores the value of a VFSS with edrophonium for diagnosing this condition.

Keywords: anti-LDL receptor-related protein 4; bulbar paralysis; double seronegative myasthenia gravis; dysphagia; videofluoroscopic swallowing study; vocal fold paralysis.

Figure 1.

Repetitive nerve stimulation test at 3 Hz in the abductor digiti minimi muscle. There was no waning.

Figure 2.

Vocal folds during the expiratory phase. The vocal folds are expected to open during expiration. However, they remained closed in our patient.

Figure 3.

A videofluoroscopic swallowing study before and after intravenous injection of edrophonium. Panels A and B show images before injection, with insufficient glottal closure (A, arrow) and residue at the base of the oral cavity and pharynx (B, arrow). Panels C and D show complete epiglottal closure (C, arrow) and no barium backflow (D, arrow) after injection. Residue at base of the pharynx (D, arrowhead).

Figure 4.

Patient’s clinical course following treatment initiation. IVIg: intravenous immunoglobulin