[Clinical and neuroelectrophysiological characteristics of primary peripheral nerve hyperexcitability syndrome]

Objective: To investigate the clinical and neuroelectrophysiological characteristics of patients with primary peripheral nerve hyperexcitability syndrome (PNHS). Methods: The clinical data of 20 patients who were diagnosed with PNHS in Beijing Tiantan Hospital from April 2016 to January 2023 were retrospectively collected. All patients underwent neuroelectrophysiological examinations. Clinical and electrophysiological characteristics were compared between the antibody positive and antibody negative groups, according to serum and cerebrospinal fluid anti-contactin-associated protein-like 2 (CASPR2) and/or anti-leucine-rich glioma-inactivated protein 1 (LGI-1) antibodies. Results: There were 12 males and 8 females, with a mean age of (44.0±17.2) years and the disease course of [M (Q₁, Q₃)] 2.3 (1.1, 11.5) months. Motor symptoms included fasciculations, myokymia, muscle pain, cramps, and stiffness. These symptoms were commonly seen in the lower limbs (17 patients), followed by upper limbs (11 patients), face (11 patients) and trunk (9 patients). Nineteen (19/20) patients had sensory abnormalities and/or autonomic dysfunction, 13 patients had central nervous system involvement, and 5 patients had concomitant lung cancer or thymic lesions. The characteristic spontaneous potentials on needle electromyography (EMG) were myokymia potential (19 patients), fasciculation potential (12 patients), spastic potential (3 patients), neuromyotonic potential (1 patients), etc, which were commonly seen in the lower limb muscles, especially the gastrocnemius muscle(12 patients). After-discharge potential was found in 8 patients, and 7 were in the tibial nerve. Seven patients had positive serum anti-CASPR2 antibodies, and 3 of them had concomitant anti-LGI1 antibodies. And 1 patient had positive serum anti-LGI1 antibody alone. Compared with patients in the antibody negative group (n=12), the patients who had anti-VGKC complex antibodies (n=8) had a shorter course of disease [M (Q₁, Q₃): 1.8 (1, 2) months vs 9.5 (3.3, 20.3) months, P=0.012], higher incidence of after-discharge potential (6/8 vs 2/12, P=0.019). The immunotherapy regimen (multi-dru, single-drug, no immunotherapy: 6, 2, 0 patients) in antibody-positive patients was different from the antibody-negative group (3, 6, 3 patients, U=21.00, P=0.023). Conclusions: The symptoms of motor nerve hyperexcitation, characteristic EMG spontaneous potentials and after-discharge potentials in PNHS patients are most commonly seen in the lower limbs. Attention should be paid to concomitant sensory and autonomic nerve hyperexcitation. PNHS patients with positive serum anti-CASPR2 antibodies may require immunotherapy with multiple drugs.