1514 - Seronegative Myasthenia Gravis: Overcoming Diagnostic Uncertainty Through Therapeutic Trial

Thursday, February 19, 2026

5:00 PM - 6:30 PM AST

Presenting Author(s)

MK

Mohamad Kaki, DO

D.O.
Memorial Healthcare System
Boca Raton, Florida, United States

Corresponding Author(s)

NC

Neenu Cherian, MD

Attending Physician
Memorial Healthcare System
Hollywood, Florida, United States
JP

Julian Perez, DO

Resident physician
Memorial healthcare systems
Davie, Florida, United States

Submitter(s)

MK

Mohamad Kaki, DO

Memorial Healthcare System
Boca Raton, Florida, United States

Case Diagnosis: Seronegative Myasthenia Gravis

Case Description: We present the case of a 70-year-old female with a history of renal transplant admitted with severe generalized weakness after hospitalization for urosepsis. Her medical history is notable for remote episodes of ptosis and neck weakness that previously improved with plasmapheresis. Prior outpatient workup included nerve conduction study showing a borderline decremental response on repetitive stimulation, while serologic testing for AChR, MuSK, and LRP4 antibodies was negative on two occasions. Before hospitalization, the patient was functionally independent. Upon transfer to rehabilitation, she required moderate assistance for activities of daily living and maximal assistance for ambulation. She was started on pyridostigmine 60 mg, which led to significant improvement in her weakness. By discharge, she reached modified independence with ambulation and full independence in activities of daily living.

Discussions: Myasthenia gravis (MG) is an autoimmune disorder characterized by antibodies targeting components of the postsynaptic neuromuscular junction. True seronegative MG accounts for only about 5-10% of cases and presents significant diagnostic challenges. Electrophysiologic studies can aid in diagnosis; however, in our patient, EMG findings were inconclusive and serologic testing was negative, leaving uncertainty. Given the clinical suspicion, a trial of pyridostigmine was initiated, resulting in marked improvement in mobility and overall function. This case underscores the importance of early recognition and management of MG to reduce functional impairment. Furthermore, in diagnostically challenging cases, initiating acetylcholinesterase inhibitor therapy can serve as both a diagnostic tool and a therapeutic intervention.

Conclusions: This case demonstrates the diagnostic challenges of seronegative myasthenia gravis and emphasizes the value of clinical judgment when laboratory and electrophysiologic findings are inconclusive. Initiation of acetylcholinesterase inhibitor therapy facilitated significant functional recovery in our patient and provided diagnostic clarity. Prompt recognition and treatment of MG, even in the absence of confirmatory testing, are critical to minimizing disability and optimizing patient outcomes.