Abstract
RATIONALE: The coexistence of paraneoplastic neurological syndrome (PNS) and Guillain-Barré syndrome (GBS) is an extremely rare clinical entity, and misdiagnosis is prevalent in grassroots healthcare settings due to limited diagnostic resources and atypical clinical presentations. Clarifying the diagnostic pathway for such overlap syndromes is critical to improving management in resource-limited primary care institutions. PATIENT CONCERNS: A 75-year-old male presented with 4 months of persistent left facial numbness and 2 months of progressive distal limb numbness, accompanied by an unsteady gait and an unintentional 20 kg weight loss over 4 months. He was initially misdiagnosed with trigeminal neuritis and chronic inflammatory demyelinating polyneuropathy and had a history of hyperlipidemia managed with atorvastatin. DIAGNOSES: Serum anti-Hu antibody testing returned positive, while cerebrospinal fluid ganglioside antibodies were negative. Chest computed tomography identified mediastinal lymphadenopathy, and subsequent positron emission tomography-computed tomography revealed a hypermetabolic nodule in the right lower lung suggestive of primary malignancy. Bronchoscopic biopsy and immunohistochemistry confirmed small-cell lung carcinoma (SCLC). The final diagnosis was anti-Hu-positive PNS overlapping with GBS, secondary to SCLC, despite the absence of classic GBS clinical and laboratory features. INTERVENTIONS: The patient received intravenous methylprednisolone pulse therapy (500 mg/d, tapered per clinical response), adjunctive gastrointestinal protection (pantoprazole), calcium/potassium supplementation, lipid-lowering therapy (atorvastatin), and neuroprotective agents (α-lipoic acid, methylcobalamin, vitamin B1). A multidisciplinary team coordinated neuro-oncological management following the SCLC diagnosis. OUTCOMES: During follow-up, the patient achieved a favorable recovery with significant alleviation of neurological symptoms, despite the SCLC's high Ki-67 proliferation index (90%), attributed to early diagnostic confirmation and coordinated multidisciplinary care. LESSONS: For patients with subacute neuropathy and unexplained weight loss in primary care settings, routine paraneoplastic antibody testing and whole-body imaging (e.g., positron emission tomography-computed tomography) are essential to facilitate early recognition of PNS-GBS overlap syndromes. Multidisciplinary collaboration across neurology, oncology, and radiology is key to timely management and improved prognosis in resource-limited healthcare environments, even in the absence of classic disease phenotypes.