Methotrexate neuropathy typically appears as sudden stroke-like symptoms, progressive weakness in the limbs, or sensory disturbances, and it can look so much like a genuine stroke or other neurological emergency that even experienced clinicians sometimes get the diagnosis wrong initially. The drug, used widely in chemotherapy for leukemia, lymphoma, and osteosarcoma, interferes with folate metabolism in ways that can damage the brain, spinal cord, and peripheral nerves. Recognizing the pattern of symptoms and knowing which imaging and electrodiagnostic tests to order makes the difference between a prompt diagnosis and days of misguided treatment.
The Stroke-Like Presentation
The most recognizable form of methotrexate neurotoxicity mimics an acute stroke. Patients develop sudden hemiparesis (weakness on one side of the body), speech problems, or altered consciousness, often within days of receiving the drug. An Italian multi-center case series of 11 pediatric patients found that about 73% had speech disorders such as aphasia or dysarthria, roughly 64% developed limb weakness, and about 27% experienced full hemiplegia. Other symptoms in that cohort included tongue deviation, altered mental status, tremors, and even seizures.1PubMed Central. The Clinical Impact of Methotrexate-Induced Stroke-Like Neurotoxicity in Paediatric Departments: An Italian Multi-Centre Case-Series A separate case report described an 18-year-old woman with acute lymphoblastic leukemia who developed a sudden neurological deficit that was initially worked up as a cerebrovascular event before methotrexate toxicity was identified.2PubMed Central. Methotrexate-Induced Stroke-Like Encephalopathy: Beware the Stroke Mimic
The clinical challenge here is timing and context. These patients are often already hospitalized for cancer treatment, and many have reasons to be at risk of genuine stroke (central lines, thrombocytopenia, coagulopathy). A clinician seeing sudden-onset aphasia and hemiparesis in a cancer patient will reasonably think “stroke” before “drug side effect.” The distinction matters enormously, because the treatments diverge completely. Clinicians handling patients on methotrexate who develop acute stroke-like symptoms need a high index of suspicion for drug-related neurotoxicity to avoid chasing the wrong diagnosis.3PubMed Central. Recurrence of methotrexate-induced leukoencephalopathy after methotrexate rechallenge: A case report and literature review
Myelopathy and Peripheral Nerve Involvement
Not all methotrexate neurotoxicity hits the brain. Intrathecal administration, where the drug is injected directly into the spinal fluid, can damage the spinal cord and nerve roots. One case report described a 39-year-old man with B-cell acute lymphoblastic leukemia who developed bilateral foot tingling and progressive leg weakness after intrathecal methotrexate. His nerve conduction studies and clinical picture initially looked so much like Guillain-Barré syndrome that it became the working diagnosis before the true cause was identified.4PubMed Central. Progressive Lower Extremity Paralysis Caused by Intrathecal MTX-Induced Myelopathy Mimicking Guillain-Barre Syndrome: A Case Report
Subacute myelopathy from methotrexate follows a different tempo. Rather than a sudden event, it builds over weeks, progressively causing leg paralysis, sensory loss, and loss of bladder and bowel control. A study of 13 leukemia patients treated with intrathecal methotrexate found that their symptoms resembled subacute combined degeneration, a pattern usually caused by vitamin B12 deficiency, complete with dorsal column hyperintensity on MRI. The critical clue was that, unlike true B12 deficiency, these cases did not improve with cobalamin supplementation.5Arşiv Kaynak Tarama Dergisi. Systemic Effects of Methotrexate upon the Peripheral Nerve Tissue
Direct nerve root damage is another possibility. A case report of acute lumbar polyradiculoneuropathy after intrathecal methotrexate emphasized that absent lumbosacral F-wave motor responses, without the typical demyelinating pattern you would expect in Guillain-Barré, pointed to direct chemical injury to the nerve roots rather than an autoimmune process.6PubMed Central. Acute lumbar polyradiculoneuropathy as early sign of methotrexate intrathecal neurotoxicity: Case report and literature review
Why Methotrexate Damages Nerve Tissue
Methotrexate works by blocking folate metabolism, which is why it kills rapidly dividing cancer cells. Unfortunately, folate metabolism is also essential for healthy nerve function. When methotrexate disrupts folate pathways, it reduces the availability of a compound called 5-methyltetrahydrofolate, which neurons need to convert homocysteine into methionine. The result is a buildup of homocysteine in the nervous system.7PubMed Central. Methotrexate encephalopathy: Two cases in adult cancer patients, who recovered with pathophysiologically based therapy Homocysteine is directly toxic to blood vessel walls and overstimulates a particular receptor on neurons (the NMDA receptor), which triggers oxidative damage and can kill nerve cells.8PubMed. Dextromethorphan is effective in the treatment of subacute methotrexate neurotoxicity
The biochemistry has other layers. Methotrexate also interferes with adenosine metabolism, excitatory amino acid pathways, and biopterin synthesis. Researchers have suggested that the acute form of neurotoxicity, the sudden stroke-like episodes, may be partly driven by adenosine-related mechanisms, while the more slowly developing forms involve homocysteine accumulation and its downstream effects on neurotransmitters.9Chemotherapy. Biochemical and Clinical Aspects of Methotrexate Neurotoxicity Animal research has additionally implicated thinning of the myelin sheath around nerves, axonal degeneration, and mitochondrial dysfunction as consequences of methotrexate exposure.5Arşiv Kaynak Tarama Dergisi. Systemic Effects of Methotrexate upon the Peripheral Nerve Tissue
Who Is Most at Risk
Two factors stand out when predicting who will develop methotrexate neurotoxicity: the route of administration and the patient’s age.
A 2024 analysis of 498 patients found an overall neurotoxicity rate of about 5%. Children under 18 were hit harder, with roughly 7.4% affected compared to about 3.1% of adults, translating to about 2.5 times the odds for pediatric patients. The presentations also differed strikingly by age. Every affected child in the study developed encephalopathy (the brain-based form), while adult presentations were more varied, including myelopathy and radiculopathy as well.10PubMed Central. Potential neurotoxicity associated with methotrexate
Route of administration matters too, and the pattern flips between children and adults. In pediatric patients from the same study, intravenous methotrexate carried the highest neurotoxicity rate (about 21%), significantly exceeding both the intrathecal route (about 5%) and the combined route (10%). In adults, the pattern reversed: intrathecal administration had the highest rate (20%), compared to roughly 1% for intravenous and 3% for the combined route.10PubMed Central. Potential neurotoxicity associated with methotrexate This discrepancy likely reflects differences in drug dosing protocols, blood-brain barrier permeability, and the specific cancers treated in each age group, though the exact reasons remain debated.
What Brain Imaging Shows
Standard CT scans of the head are often unremarkable in the acute phase, which is one reason methotrexate neurotoxicity gets initially misdiagnosed. The imaging modality that picks up early changes is diffusion-weighted MRI (DWI), which detects restricted water movement in brain tissue.
In a study of six children with early methotrexate neurotoxicity, DWI showed abnormal restricted diffusion in the centrum semiovale, a white matter region deep in the brain, in every patient. This finding correlated with the acute onset of hemiparesis or speech problems. A standard fluid-attenuated MRI sequence (FLAIR) was negative during the acute episode but became positive on follow-up imaging, meaning DWI catches changes that other MRI sequences miss in the critical early window.11American Journal of Neuroradiology. Diffusion-Weighted MR Imaging of Early Methotrexate-Related Neurotoxicity in Children
The DWI lesions have a distinctive appearance. They show up as bright, well-defined areas within the subcortical white matter, and they cross vascular territory boundaries, something true strokes almost never do. This geographic pattern is a key diagnostic clue. Even more reassuringly, the DWI abnormalities often resolve completely within one to four days as symptoms improve.12PubMed. Diffusion-weighted MRI correlates of subacute methotrexate-related neurotoxicity A true ischemic stroke would not behave this way on serial imaging.
The Broader Diagnostic Workup
Imaging alone does not always clinch the diagnosis, and the workup often needs to extend further. In one reported case, a patient undergoing evaluation for methotrexate neurotoxicity had a normal cerebrospinal fluid analysis, no epileptic activity on EEG, and an unremarkable CT scan. Nerve conduction studies, however, revealed mildly prolonged F-waves and a slightly reduced sensory nerve action potential in the sural nerve, subtle findings that offered electrodiagnostic evidence of peripheral nerve involvement.13Clinical Neurophysiology Practice. Methotrexate-induced neurotoxicity: Diagnostic challenges and the role of neurophysiological testing
Electromyography (EMG) and nerve conduction studies can be valuable when the presentation involves the spinal cord or peripheral nerves rather than the brain. As noted in the lumbar polyradiculoneuropathy case, early EMG screening detected absent F-wave responses that pointed to direct nerve root toxicity before other tests showed anything abnormal.6PubMed Central. Acute lumbar polyradiculoneuropathy as early sign of methotrexate intrathecal neurotoxicity: Case report and literature review In practice, the diagnosis of methotrexate neuropathy is usually one of exclusion: the clinician rules out stroke, infection, tumor progression, and autoimmune conditions, then correlates the timing of symptoms with drug exposure and supporting findings on imaging or electrodiagnostic testing.
Genetic Factors That Raise Susceptibility
Not everyone exposed to methotrexate develops neurotoxicity, and genetics play a role in who does. The MTHFR gene encodes an enzyme central to folate metabolism, and certain variants of this gene reduce its efficiency. A study of patients with primary central nervous system lymphoma treated with methotrexate-based therapy found that the MTHFR 1298A>C variant was associated with both increased frequency and greater severity of leukoencephalopathy over time. That particular genotype predicted treatment-induced white matter damage with a sensitivity of about 71% and a specificity of about 62%.14Journal of Clinical Oncology. MTHFR polymorphisms and neurotoxicity and overall survival after methotrexate-based therapy in primary CNS lymphoma
These numbers are not strong enough to use as a standalone screening tool, but they suggest that patients who are already known to carry MTHFR variants might warrant closer neurological monitoring during methotrexate therapy. Genetic testing for MTHFR status is inexpensive and widely available, and it could eventually become part of a risk-stratification approach for patients about to receive high-dose methotrexate regimens.
Treatment and Prevention
For acute methotrexate neurotoxicity, several treatments have been tried, but the evidence for most of them is complicated by the fact that many episodes resolve on their own. Dextromethorphan (commonly found in over-the-counter cough medicines) has been used based on the rationale that it blocks the NMDA receptor, which is overstimulated by the homocysteine buildup. Other agents that have been tried include dexamethasone, aminophylline, and folinic acid, though because most stroke-like episodes resolve spontaneously, the actual benefit of these medications remains unclear.1PubMed Central. The Clinical Impact of Methotrexate-Induced Stroke-Like Neurotoxicity in Paediatric Departments: An Italian Multi-Centre Case-Series
Prevention is a more promising angle. Folinic acid (leucovorin) “rescue” given after high-dose methotrexate is already standard practice in oncology, but there is a strong argument that many cases of neurotoxicity result from rescue that is too little or too late. A review of published data concluded that when folinic acid is given in sufficiently high doses, starting 24 to 36 hours after methotrexate exposure, virtually all forms of post-methotrexate neurotoxicity can be prevented without compromising the drug’s cancer-killing effectiveness.15PubMed. Neurotoxicity after high-dose methotrexate (MTX) is adequately explained by insufficient folinic acid rescue A comprehensive review of neuropsychological studies reached a similar conclusion, finding that inadequate folinic acid rescue was the cause of neurocognitive damage and that adequate rescue prevented it.16Journal of Pediatric Hematology/Oncology. A Comprehensive Review of Neuropsychologic Studies Supports the Concept That Adequate Folinic Acid Rescue Prevents Post Methotrexate Neurotoxicity
For situations where methotrexate levels remain dangerously elevated, for instance after an accidental overdose, more aggressive measures exist. Glucarpidase (carboxypeptidase-G2) is an enzyme that rapidly degrades methotrexate in the bloodstream. In one case, it produced an 86% decline in methotrexate concentration, outperforming extracorporeal clearance methods like dialysis.17PubMed. Treatment of methotrexate intoxication with various modalities of continuous extracorporeal therapy and glucarpidase In two pediatric patients who received accidental intrathecal methotrexate overdoses and developed acute confusion, pain, and seizures, a combination of cerebrospinal fluid exchange, intravenous dexamethasone, folinic acid, and intrathecal glucarpidase was used. At three-year follow-up, one patient had no neurological or neuropsychological sequelae, while the other reported some short-term memory problems.18PubMed. Treatment of two cases on the same day of intrathecal methotrexate overdose using cerebrospinal fluid exchange and intrathecal instillation of carboxypeptidase-G2
Long-Term Neurological Outlook
The good news for most patients who experience acute methotrexate neurotoxicity is that symptoms resolve. A large study tracking children treated for acute lymphoblastic leukemia found no mortality attributable to long-term neurological problems from methotrexate neurotoxicity over a median follow-up of nearly eight years. About 1.3% of those with available long-term data were diagnosed with epilepsy at last follow-up, and three of the seven children with epilepsy had experienced symptomatic neurotoxicity episodes; all remained in first complete remission for their leukemia.19Haematologica. Methotrexate-related central neurotoxicity: clinical characteristics, risk factors and genome-wide association study in children treated for acute lymphoblastic leukemia
The picture gets more nuanced when you look at brain imaging over time. A study of osteosarcoma patients who received high-dose methotrexate found that while acute symptoms resolved in all but one patient, MRI leukoencephalopathy (white matter changes visible on brain scans) was present in 83% of patients during treatment. Among those who had MRI scans three or more years after finishing treatment, white matter changes persisted in most, though often at a milder grade. The severity of leukoencephalopathy was linked to receiving more than 12 courses of methotrexate and to severe depression, but not to the acute neurotoxicity episodes themselves. Neurocognitive testing showed IQ scores within normal ranges, except for processing speed, which was reduced during treatment but improved afterward. At a median follow-up of eight and a half years, most patients had integrated into school or employment.20PubMed. Leukoencephalopathy, a Frequent Complication After High-Dose Methotrexate in Treatment of Osteosarcoma
The gap between what the brain scans show and how patients actually function is worth paying attention to. White matter changes on MRI sound alarming, and they are common, but they do not necessarily translate into meaningful cognitive impairment for most patients. The area where residual effects seem most consistent is processing speed, the ability to quickly take in and respond to information, which may subtly affect academic performance or workplace efficiency even when overall intelligence remains intact.