Recent breakthroughs in Vision-Language Models (VLMs) have shown strong potential in medical analysis, but they remain limited in the brain lesion image domain, especially when pathological regions occupy a small portion of the image. This is because VLMs tend to put excessive attention on background regions that are visually similar to target regions. Based on the findings, we propose SAM-GPT, a novel framework that leverages segmentation-derived spatial priors to support VLM-based lesion classification. It first uses an enhanced segmentation model to localize pathological regions for diagnostic tasks, and then converts lesion attributes (e.g., size, pixel range, lesion location) into linguistic guidance for a vision–language model. To improve small lesion recognition, we incorporate a new Hilbert scanning method into Mamba that improves both local spatial continuity and global spatial modeling. Experiments on benchmark datasets show that our model achieves an average Dice coefficient of 72.80% on the brain lesion segmentation task and an accuracy of 80.56% on the brain disease classification task, demonstrating the effectiveness of the proposed framework. The code is available at https://github.com/1JF-Wang/sam-gpt.