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BACKGROUND Numb chin syndrome, a clinical manifestation of mental nerve neuropathy, presents with pain, numbness, or altered sensation in the mental nerve distribution. While most cases are dental or traumatic, it can signal an underlying malignancy. CASE REPORT A 57-year-old woman presented with a 2-year history of pain and hypesthesia in the left mental nerve distribution. Initial contrast-enhanced MRI showed mild bone marrow edema near the left mental foramen, which was interpreted in the radiology report as inflammatory change without a definite mass. Due to persistent symptoms, limited incisional biopsy was conducted in private practice, suggested a neuroma and likely reflecting non-representative sampling. Repeat MRI demonstrated a suspicious lesion involving the mental nerve region and the left submandibular gland with cervical lymphadenopathy. After referral to our department, ultrasound confirmed homogeneous lesions in the submandibular gland and near the mental foramen. The patient underwent surgical exploration including a targeted perilesional excision with partial osteotomy, accompanied by removal of adjacent lymph nodes and submandibular gland. Histopathology confirmed nodal marginal zone lymphoma. Staging CT showed disseminated nodal involvement and bone marrow densification without extranodal involvement. The patient developed severe mandibular pain consistent with nerve compression and received localized radiotherapy and rituximab, resulting in marked symptom relief. CONCLUSIONS This case illustrates how subtle imaging findings and non-representative biopsy can lead to diagnostic delay in malignancy-associated numb chin syndrome. Persistent unilateral mental nerve neuropathy should prompt careful reassessment and systemic evaluation, even in the absence of clear radiological or histological evidence, to enable timely diagnosis and appropriate management.