A Case of Peripheral Nerve Hyperexcitability Syndrome Pretended as Infective Endocarditis: Case Report

Background: The peripheral nerve hyperexcitability (PNH) syndromes cause repetitive spontaneous electrical discharges in peripheral nerves (mainly motor axons), which leads to the increased activity of the innervated area. PNH syndromes develop various motor, sensory, and autonomous symptoms, of which motor symptoms are the most considerable, including cramps, fasciculations, and myokymia. The PNH syndromes are classified into cramp-fasciculation syndrome, neuromyotonia (Isaacs syndrome), and Morvan’s syndrome. Morvan syndrome is associated with the involvement of the central nervous system (CNS). PNH syndromes primarily result from dysfunction of voltage-gated potassium channels (VGKC), mainly due to autoantibodies. Alternative causes have been proposed, including potential infectious origins. Previous studies have associated staphylococcal abscesses and Hepatitis B Virus (HBV) infections with the pathogenesis of Isaacs syndrome rather than Morvan’s syndromes. Case Presentation: We present a case of VGKC-antibody-positive PNH presented by symptoms such as fatigue, fever, chills, dyspnea, weight loss, hyperhidrosis, spontaneous muscle spasms, and cramps in the lower limbs. Central Nervous System (CNS) involvement included hallucinations, sleep disorders, confusion, and mood alterations, along with vegetation in the right atrium as detected by echocardiography. The patient initially received a two-week course of antibiotic therapy for suspected infective endocarditis (IE) and bacteremia. Subsequently, due to persistent symptoms despite antibiotic treatment, electromyography (EMG) was performed, revealing anti-VGKC antibodies. The patient then underwent several plasma exchanges and was prescribed carbamazepine, resulting in a significant improvement in their condition. Conclusion: This case shares similarities with previous cases of PNH syndrome (especially Morvan’s syndromes) triggered by infections other than previously reported, suggesting that autoantibodies against pathogens may be responsible for the manifestation of PNH syndrome. Moreover, the dramatic response to plasmapheresis and removal of antibodies, as well as positive Anti-CASPR2 auto-antibody, confirms our diagnosis.