Irinotecan-Induced Transient Dysarthria in a Patient With Metastatic Colorectal Cancer: A Case Report.

We present a rare case of irinotecan-induced transient dysarthria in a 60-year-old female undergoing FOLFIRI (folinic acid (leucovorin), fluorouracil (5-FU), and irinotecan) chemotherapy for metastatic colorectal cancer. In eight out of the 12 cycles, an isolated, self-limiting "lingual dysarthria" with tongue stiffness consistently occurred during infusion and resolved promptly upon completion. Cranial imaging done during the initial episode and after the completion of the chemotherapy regimen were unremarkable. This temporal correlation suggests a drug-induced effect, proposed to be related to cholinergic hyperactivity associated with the drug's reversible inhibition of acetylcholinesterase. The hypoglossal nucleus, responsible for the motor function of the tongue, is selectively affected due to dense innervation by muscarinic cholinergic receptors (in comparison to other brainstem nuclei). This aligned with acute cholinergic syndrome common to irinotecan, and dysarthria might just be a rare manifestation of this common phenomenon. Its reversibility and atropine responsiveness support the cholinergic hypothesis. Clinicians should be mindful of this rare adverse event to avoid premature cessation of effective chemotherapy. Patient education on potential side effects and a comprehensive dysarthria work-up are crucial.