Monoparesis as a Conversion Disorder in Borderline Personality Disorder

Background: Borderline Personality Disorder (BPD) is a complex psychiatric disorder marked by unstable relationships, mood lability, and a shattered self-image, presenting with comorbid conditions across a variety of clinical contexts. The diverse nature of its symptoms manifests across a broad spectrum, including atypical neurological manifestations in the form of a conversion disorder as transient monoparesis. Case Presentation: We report a case of a 21-year-old African American with posttraumatic stress disorder, and alcohol and cannabis use disorders. She presented voluntarily with a sudden onset of weakness in the left lower extremity following a dispute with her boyfriend. Psychiatric evaluation identified the classic BPD features: self-injury, impulsiveness, unstable relationships, and mood instability. Neurological system examination was significant for 3/5 muscle strength of the left lower extremity. Laboratory investigations, CT scan of the head, and lumbar spine were normal. However, urine toxicology tested positive for cannabinoids. A follow-up re-evaluation of left lower extremity muscle strength showed a power of 5; the patient was able to ambulate with no restrictions. Discussion: This patient presents features consistent with the diagnostic criteria of BPD, including impulsive actions, self-harm, and disputes with her boyfriend. This case highlights the unusual neurological manifestation of BPD featuring transient monoparesis. The literature documents neurological symptoms in BPD, but monoparesis remains an infrequent manifestation. The finding of a lack of a physiological cause and the patient’s swift recovery highlight a conversion disorder, an atypical presentation of BPD. These atypical symptoms reinforce the diagnostic complexity of BPD and the need for a holistic evaluation of BPD patients. Conclusion: Healthcare professionals should recognize that BPD may present with rare neurological symptoms. Though a conversion disorder in feature, a complete neurological examination should accompany the initial clinical examination.