PMC9720310_01
Kidney biopsy findings showing stage I membranous nephropathy (A-C). (A) Normal mesangial cellularity (periodic acid-Schiff; original magnification, x100). (B) Slight global glomerular basement membrane thickening (yellow arrows; Jones methenamine silver; original magnification, x400). (C) Subepithelial electron-dense deposits, partially in the glomerular basement membrane (yellow arrows; original magnification, x4,000). (D) Skin lesions on the patient's left upper arm. (E, F) Skin biopsy findings showing cutaneous amyloidosis. (E) The skin specimen stained by hematoxylin-eosin revealed parakeratosis with focal hyperkeratosis, widened dermal papilla, and an amorphous red-stained mass substance (yellow arrow; x400). (F) The skin specimen stained by crystal violet was positive (yellow arrow; x400).
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Based on the above observations, the patient was diagnosed with stage I membranous nephropathy ( Figure 1 ). This patient also underwent skin biopsy, where pathology showed cutaneous amyloidosis ( Figure 1 ).
(A) Chest CT showing a thymic mass in the left anterior mediastinum (yellow arrow). (B) LGI1 antibody cell-based assay showing a 1:32 positive ratio. (C) ECG showing acute anterior, lateral, and high lateral myocardial infarction-like ECG changes. (D) Afterdischarges were observed in the F wave. (E) Needle EMG showing duplet, triplet, and multiplet bursts of spontaneous motor unit discharges in the tested muscles of the limbs at rest suggestive of myokymia. CT, computed tomography; LGI1, leucine-rich glioma-inactivated 1; ECG, electrocardiogram; EMG, electromyography.
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The patient underwent chest computed tomography (CT), which revealed a thymic mass in the left anterior mediastinum ( Figure 2 ). During this period, his ECG showed acute anterior, lateral, and high lateral myocardial infarctions ( Figure 2 ); however, the myocardial enzyme profile and troponin levels were normal, and he had no symptoms of precardiac discomfort. Needle electromyography (EMG) showed duplet, triplet, and multiplet bursts of spontaneous motor unit discharges in the tested muscles of the limbs at rest, and after discharges were observed in the F wave, suggesting peripheral nerve hyperexcitability syndrome ( Figure 2 ). The patient's serum was also tested for antibodies to cell-surface antigens, including N-methyl-D-aspartate receptor, LGI1, contactin-associated protein 2 (CASPR2), GABABR, and alpha-amino-3-hydroxy-5-methyl-4-iso-xazolepropionic acid (AMPA) receptors (EUROIMMUN, Germany), and the results showed that antibodies against LGI1 and GABABR were both positive, with titers of 1:32 ( Figure 2 ) and 1:10, respectively.
Timeline of the diagnosis, treatment, and outcome. CT, computed tomography; cMAP, compound muscle action potential responses.
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The timeline of the diagnosis and treatment is shown in  Figure 3 .