Dissemination in time as a requirement for diagnosis of multiple sclerosis: Time for a change?

The requirement to demonstrate dissemination in time (DIT) in order to diagnose multiple sclerosis (MS) has been enshrined in the literature since earliest efforts to establish diagnostic critera. However, various diagnostic criteria over the years, including the 2017 McDonald criteria, have inconsistently utilized this concept. This Viewpoint contends that current criteria for DIT are inadequate and sometimes inappropriate. It recommends continuing to consider DIT in the diagnosis of MS, but advocates utilizing all available information with high specificity for the disease, including the presence of large numbers of typical lesions, to make the diagnosis. This approach enables early initiation of disease-modifying treatment in situations with a favorable risk-benefit ratio.

Effects of teriflunomide treatment on cognitive performance and brain volume in patients with relapsing multiple sclerosis: Post hoc analysis of the TEMSO core and extension studies.

BACKGROUND: In post hoc analyses of Teriflunomide Multiple Sclerosis Oral study (TEMSO; NCT00134563), teriflunomide 14 mg significantly reduced brain volume loss (BVL) versus placebo in patients with relapsing multiple sclerosis (MS). OBJECTIVE: In this post hoc analysis of TEMSO and its long-term extension (NCT00803049), we examined the relationship between teriflunomide's effects on BVL and cognition. METHODS: We analyzed data from 709 patients who received teriflunomide 14 mg in TEMSO or its extension. The change in cognitive performance, assessed using the Paced Auditory Serial Addition Test 3 (PASAT-3), was measured in subgroups stratified by BVL over 2 years (least BVL: ⩽ 0.52%; intermediate BVL: >0.52%-2.18%; most BVL: >2.18%). BVL, MRI lesions, and relapses over 2 years were evaluated as potential mediators of the effect of teriflunomide on cognition. RESULTS: Teriflunomide 14 mg significantly improved PASAT-3 Z-scores versus placebo through year 2. In the least- and intermediate-BVL groups, significant improvements in PASAT-3 Z-score were demonstrated versus the most-BVL group over 3 years in the extension. According to the mediation analysis, 44% of the teriflunomide effect on cognition was due to effects on BVL at year 2. CONCLUSION: Teriflunomide improves cognition largely through its effects on BVL. Accelerated BVL earlier in the disease course may predict cognitive outcomes. CLINICALTRIALS.GOV IDENTIFIER: NCT00134563, NCT00803049.

A Phase 3, double-blind, placebo-controlled efficacy and safety study of ADS-5102 (Amantadine) extended-release capsules in people with multiple sclerosis and walking impairment.

BACKGROUND: ADS-5102, a delayed-release, extended-release (DR/ER) amantadine, improved walking speed in MS in a Phase 2 trial. OBJECTIVE: The aim of this study was to present primary results of a Phase 3, double-blind, ADS-5102 trial (INROADS) for walking speed. METHODS: Adult participants with MS and walking impairment, not currently using amantadine or dalfampridine, underwent 4-week placebo run-in before randomization 1:1:1 to placebo, 137 or 274 mg/day ADS-5102 for 12 weeks. Primary outcome was the proportion of responders (20% increase in Timed 25-Foot Walk (T25FW) speed) for 274 mg ADS-5102 versus placebo at end of double-blind (Study Week 16). Additional measures included Timed Up and Go (TUG), 2-Minute Walk Test (2MWT), and 12-item Multiple Sclerosis Walking Scale (MSWS-12). RESULTS: In total, 558 participants were randomized and received double-blind treatment. Significantly more participants responded with 274 mg ADS-5102 (21.1%) versus placebo (11.3%). Mean T25FW speed also significantly improved (0.19 ft/s) versus placebo (0.07 ft/s). Other measures were not significant using prespecified hierarchical testing procedure. Adverse events led to discontinuation for 3.8% (placebo), 6.4% (137 mg ADS-5102), and 20.5% (274 mg ADS-5102). CONCLUSION: INROADS met its primary endpoint, showing a significantly greater proportion of participants with meaningful improvement in walking speed for 274 mg ADS-5102 versus placebo. Numeric dose response was seen for some secondary efficacy outcomes and adverse events.

Hippocampal volume is more related to patient-reported memory than objective memory performance in early multiple sclerosis.

BACKGROUND: When persons with multiple sclerosis (MS) report memory decline but objective memory performance is normal, there is a bias toward believing objective test results. OBJECTIVE: Investigate whether subjective memory decline or objective memory performance is more related to hippocampal and hippocampal subfield volumes in early MS. METHODS: Persons with early MS (n = 185; ⩽5.0 years diagnosed) completed a subjective memory questionnaire; an objective memory composite was derived from four memory tests. Total hippocampal and subfield volumes were derived from high-resolution 3.0 T magnetic resonance images (MRIs). Partial correlations assessed links between hippocampal volumes and both subjective and objective memory, controlling for age, sex, mood, and pre-morbid intelligence quotient (IQ). RESULTS: Lower total hippocampal and CA1 volumes were related to worse subjective memory but not objective memory (controlling for multiple comparisons). Correlations between subjective memory and both CA1 and subiculum were significantly stronger than were correlations between objective memory and these subfields. Patients in the worst tertile of subjective memory complaints (but not objective memory) had lower hippocampal volumes than 35 demographically similar healthy controls. CONCLUSION: Patient-report is inherently a longitudinal assessment of within-person memory change in everyday life, which may be more sensitive to subtle disease-related changes than cross-sectional objective tests. Findings align with the aging literature.

Depression and cognitive function in early multiple sclerosis: Multitasking is more sensitive than traditional assessments.

BACKGROUND: Persons with multiple sclerosis (MS) and depression symptoms report real-world cognitive difficulties that may be missed by laboratory cognitive tests. OBJECTIVE: To examine the relationship of depressive symptoms to cognitive monotasking versus multitasking in early MS. METHOD: Persons with early MS (n = 185; ⩽5 years diagnosed) reported mood, completed monotasking and multitasking cognitive tests, and received high-resolution 3.0 T magnetic resonance imaging (MRI). Partial correlations analyzed associations between mood and cognition, controlling for age, sex, estimated premorbid IQ, T2 lesion volume, and normalized gray matter volume. RESULTS: Depression symptoms were more related to worse cognitive multitasking (-0.353, p < 0.001) than monotasking (r = -0.189, p = 0.011). There was a significant albeit weaker link to cognitive efficiency composite score (r = -0.281, p < 0.001), but not composite memory (r = -0.036, p > 0.50). Findings were replicated with a second depression measure. Multitasking was worse in patients with at least mild depression than both patients with no/minimal depression and healthy controls. Multitasking was not related to mood in healthy controls. CONCLUSIONS: Depression symptoms are linked to cognitive multitasking in early MS; standard monotasking cognitive assessments appear less sensitive to depression-related cognition. Further investigation should determine directionality and mechanisms of this relationship, with the goal of enhancing treatment for cognitive dysfunction and depression in MS.

Characterizing lymphocyte counts and infection rates with long-term teriflunomide treatment: Pooled analysis of clinical trials.

BACKGROUND: In Phase 3 studies, teriflunomide reduced relapse rates and disability progression compared with placebo; however, decreases in lymphocyte counts were also observed. OBJECTIVE: To describe the effect of long-term teriflunomide treatment on lymphocyte counts and infection rates among patients in pooled analyses of Phase 3 core and extension studies. METHODS: Four randomized trials (TEMSO, TOWER, TENERE, and TOPIC) compared teriflunomide 7 mg or 14 mg treatment with either placebo and/or subcutaneous interferon (IFN) ß-1a 44 µg in patients with relapsing forms of multiple sclerosis (MS) (or first clinical episode suggestive of MS in TOPIC). RESULTS: In 1895, patients ever exposed to teriflunomide, mean (standard deviation) absolute lymphocyte counts declined from Week 0 (1.89 (0.59)) to Week 24 (1.67 (0.52)) and then remained stable thereafter. In the core plus extension studies (up to 10.7 years), 7.3% and 2.2% experienced Grade 1 and Grade 2 lymphopenia, respectively. Infections were reported in 56.9% of patients without lymphopenia, 60.9% with Grade 1 lymphopenia, and 54.8% with Grade 2 lymphopenia. Serious infections occurred in 3.7%, 4.3%, and 7.1%, respectively. CONCLUSION: Long-term risk of lymphopenia and infections in patients who continue to receive teriflunomide is low, demonstrating a limited impact on adaptive and innate immunity.

Psychological resilience is linked to motor strength and gait endurance in early multiple sclerosis.

BACKGROUND: Psychologically resilient persons persist despite obstacles and bounce back after adversity, leading to better outcomes in non-neurologic populations. It is unknown whether psychological resilience relates to objective functional outcomes in multiple sclerosis (MS). OBJECTIVE: To determine whether psychological resilience explains differential objective cognitive and motor functioning in persons with early MS. METHODS: Psychological resilience was assessed in 185 patients with early MS and 50 matched healthy controls with the Connors-Davidson Resilience Scale (CDRS-10). Subjects completed the MS Functional Composite (MSFC) and a comprehensive neurobehavioral evaluation. Correlations assessed links between CDRS-10 and MSFC, motor indices (Total, Fine Motor, Gross Motor), and cognitive indices (Total, Cognitive Efficiency, Memory). RESULTS: Higher CDRS-10 among patients was linked to better MSFC and motor outcomes (but not cognition), with the most robust relationships for gross motor function (grip strength, gait endurance). Findings were independent of mood and fatigue. CDRS-10 was unrelated to MS disease burden. CDRS-10 was also specifically linked to motor outcomes in healthy controls. CONCLUSION: Functional outcomes vary across persons with MS, even when disease burden and neurologic disability are low. These findings identify high psychological resilience as a non-disease-specific contributor to motor strength and endurance, which may explain differential outcomes across patients.

Word-finding difficulty is a prevalent disease-related deficit in early multiple sclerosis.

BACKGROUND: Persons with multiple sclerosis (MS) commonly report word-finding difficulty clinically, yet this language deficit remains underexplored. OBJECTIVE: To investigate the prevalence and nature of word-finding difficulty in persons with early MS on three levels: patient report, cognitive substrates, and neuroimaging. METHODS: Two samples of early MS patients (n = 185 and n = 55; ⩽5 years diagnosed) and healthy controls (n = 50) reported frequency/severity of cognitive deficits and underwent objective assessment with tasks of rapid automatized naming (RAN), measuring lexical access speed, memory, word generation, and cognitive efficiency. High-resolution brain magnetic resonance imaging (MRI) derived measurements of regional cortical thickness, global and deep gray matter volume, and T2 lesion volume. Relationships among patient-reported word-finding difficulty, cognitive performance, and neural correlates were examined. RESULTS: Word-finding difficulty was the most common cognitive complaint of MS patients and the only complaint reported more by patients than healthy controls. Only RAN performance discriminated MS patients with subjective word-finding deficits from those without subjective complaints and from healthy controls. Thinner left parietal cortical gray matter independently predicted impaired RAN performance, driven primarily by the left precuneus. CONCLUSION: Three levels of evidence (patient-report, objective behavior, regional gray matter) support word-finding difficulty as a prevalent, measurable, disease-related deficit in early MS linked to left parietal cortical thinning.

The efficacy of teriflunomide in patients who received prior disease-modifying treatments: Subgroup analyses of the teriflunomide phase 3 TEMSO and TOWER studies.

Teriflunomide is a once-daily oral immunomodulator approved for relapsing-remitting multiple sclerosis (MS). The objective of this post hoc analysis of the phase 3, pooled TEMSO (NCT00134563) and TOWER (NCT00751881) dataset is to evaluate the effect of teriflunomide treatment on annualised relapse rate and disability worsening across patient subgroups defined according to prior disease-modifying therapy exposure. This analysis provides further supportive evidence for a consistent effect of teriflunomide across a broad range of patients with relapsing MS, including patients who have used and discontinued other disease-modifying therapies.

Factors associated with benign multiple sclerosis in the New York State MS Consortium (NYSMSC).

BACKGROUND: This retrospective analysis explored prognostic factors associated with a benign multiple sclerosis (BMS) disease course at baseline and over the 4-year follow-up. METHODS: Patients from the centralized New York State Multiple Sclerosis Consortium registry were classified as having BMS according to 3 different criteria centered on disease duration and disability. Additional analyses explored prognostic factors associated with BMS using the most conservative disability criteria (Expanded Disability Status Scale ≤2 and disease duration ≥10 years). RESULTS: Among 6258 patients who fulfilled eligibility criteria, 19.8 % to 33.3 % were characterized as having BMS, at baseline depending on classification criteria used. Positive prognostic factors for BMS at baseline included female sex (p < 0.0001) and younger age at onset (p < 0.0001); negative prognostic factors included progressive-onset type of MS and African-American race. Of the 1237 BMS patients (per most conservative criteria), 742 were followed for a median of 4 years to explore effect of disease-modifying treatment (DMT) on benign status. DMT (p = 0.009) and longer disease duration (p = 0.007) were the only significant positive predictors of maintaining BMS at follow-up. The protective effect was stronger for patients taking DMT at both enrollment and follow-up (OR = 0.71; p = 0.006). CONCLUSIONS: There is a need for development of more reliable prognostic indicators of BMS. Use of DMT was significantly associated with maintaining a benign disease state.

Cerebrospinal fluid ceramides from patients with multiple sclerosis impair neuronal bioenergetics.

Axonal damage is a prominent cause of disability and yet its pathogenesis is incompletely understood. Using a xenogeneic system, here we define the bioenergetic changes induced in rat neurons by exposure to cerebrospinal fluid samples from patients with multiple sclerosis compared to control subjects. A first discovery cohort of cerebrospinal fluid from 13 patients with multiple sclerosis and 10 control subjects showed that acute exposure to cerebrospinal fluid from patients with multiple sclerosis induced oxidative stress and decreased expression of neuroprotective genes, while increasing expression of genes involved in lipid signalling and in the response to oxidative stress. Protracted exposure of neurons to stress led to neurotoxicity and bioenergetics failure after cerebrospinal fluid exposure and positively correlated with the levels of neurofilament light chain. These findings were validated using a second independent cohort of cerebrospinal fluid samples (eight patients with multiple sclerosis and eight control subjects), collected at a different centre. The toxic effect of cerebrospinal fluid on neurons was not attributable to differences in IgG content, glucose, lactate or glutamate levels or differences in cytokine levels. A lipidomic profiling approach led to the identification of increased levels of ceramide C16:0 and C24:0 in the cerebrospinal fluid from patients with multiple sclerosis. Exposure of cultured neurons to micelles composed of these ceramide species was sufficient to recapitulate the bioenergetic dysfunction and oxidative damage induced by exposure to cerebrospinal fluid from patients with multiple sclerosis. Therefore, our data suggest that C16:0 and C24:0 ceramides are enriched in the cerebrospinal fluid of patients with multiple sclerosis and are sufficient to induce neuronal mitochondrial dysfunction and axonal damage.

Diagnostic uncertainty during the transition to secondary progressive multiple sclerosis.

Secondary progressive multiple sclerosis (MS) is typically defined as deterioration independent of relapses for ≥ 6 months following an initial relapsing-remitting course; however, this definition is not always easily applied in clinical practice and the declaration of the change in clinical phenotype is often delayed. To identify the length of time required to re-classify relapsing-remitting MS (RRMS) patients whom have clinically transitioned to secondary progressive MS (SPMS) in clinical practice. We reviewed 123 patients with long-term follow-up and identified a sub-group whom transitioned from RRMS to SPMS, then characterized this transition period. There were 14/20 patients who transitioned during the follow-up period that had visits with uncertainty related to the clinical phenotype characterized by possible, but not definitive progression. The mean duration of this period of uncertainty was 2.9 ± 0.8 years. A period of diagnostic uncertainty regarding the transition from RRMS to SPMS existed in many of our patients. Potential reasons included the subtle nature of early progressive disease and caution in applying a progressive label, in light of the lack of evidence-based treatments as well as third-party payer concerns. Delay in definitive identification of an SPMS phenotype has a variety of implications related to patient care and research.

Constructing an adaptive care model for the management of disease-related symptoms throughout the course of multiple sclerosis--performance improvement CME.

BACKGROUND: Symptom management remains a challenging clinical aspect of MS. OBJECTIVE: To design a performance improvement continuing medical education (PI CME) activity for better clinical management of multiple sclerosis (MS)-related depression, fatigue, mobility impairment/falls, and spasticity. METHODS: Ten volunteer MS centers participated in a three-stage PI CME model: A) baseline assessment; B) practice improvement CME intervention; C) reassessment. Expert faculty developed performance measures and activity intervention tools. Designated MS center champions reviewed patient charts and entered data into an online database. Stage C data were collected eight weeks after implementation of the intervention and compared with Stage A baseline data to measure change in performance. RESULTS: Aggregate data from the 10 participating MS centers (405 patient charts) revealed performance improvements in the assessment of all four MS-related symptoms. Statistically significant improvements were found in the documented assessment of mobility impairment/falls (p=0.003) and spasticity (p<0.001). For documentation of care plans, statistically significant improvements were reported for fatigue (p=0.007) and mobility impairment/falls (p=0.040); non-significant changes were noted for depression and spasticity. CONCLUSIONS: Our PI CME interventions demonstrated performance improvement in the management of MS-related symptoms. This PI CME model (available at www.achlpicme.org/ms/toolkit) offers a new perspective on enhancing symptom management in patients with MS.

Teriflunomide versus subcutaneous interferon beta-1a in patients with relapsing multiple sclerosis: a randomised, controlled phase 3 trial.

BACKGROUND: In previous studies, teriflunomide significantly reduced the annualised relapse rate (ARR) and disability progression. OBJECTIVE: This phase 3, rater-blinded study (NCT00883337) compared teriflunomide with interferon-beta-1a (IFNß-1a). METHODS: Patients with relapsing multiple sclerosis were randomised (1:1:1) to oral teriflunomide 7-or 14 mg, or subcutaneous IFNß-1a 44 µg. The primary composite endpoint was time to failure, defined as first occurrence of confirmed relapse or permanent treatment discontinuation for any cause. Secondary endpoints included ARR, Fatigue Impact Scale (FIS) and Treatment Satisfaction Questionnaire for Medication (TSQM). The study was completed 48 weeks after the last patient was randomised. RESULTS: Some 324 patients were randomised (IFNß-1a: 104; teriflunomide 7 mg: 109; teriflunomide 14 mg: 111). No difference in time to failure was observed. There was no difference in ARR between teriflunomide 14 mg and IFNß-1a, but ARR was significantly higher with teriflunomide 7 mg. FIS scores indicated more frequent fatigue with IFNß-1a, though differences were only significant with teriflunomide 7 mg. TSQM scores were significantly higher with teriflunomide. There were no unexpected safety findings. CONCLUSION: Effects on time to failure were comparable between teriflunomide and IFNß-1a. There was no difference between teriflunomide 14 mg and IFNß-1a on ARR, though ARR was higher with teriflunomide 7 mg. The teriflunomide safety profile was consistent with previous studies.

Risk of new disease activity in patients with multiple sclerosis who continue or discontinue disease-modifying therapies (DISCOMS): a multicentre, randomised, single-blind, phase 4, non-inferiority trial.

BACKGROUND: Multiple sclerosis typically has onset in young adults and new disease activity diminishes with age. Most clinical trials of disease-modifying therapies for multiple sclerosis have not enrolled individuals older than 55 years. Observational studies suggest that risk of return of disease activity after discontinuation of a disease-modifying therapies is greatest in younger patients with recent relapses or MRI activity. We aimed to determine whether risk of disease recurrence in older patients with no recent disease activity who discontinue disease-modifying therapy is increased compared to those who remain on disease-modifying therapy. METHODS: DISCOMS was a multicentre, randomised, controlled, rater-blinded, phase 4, non-inferiority trial. Individuals with multiple sclerosis of any subtype, 55 years or older, with no relapse within the past 5 years or new MRI lesion in the past 3 years while continuously taking an approved disease-modifying therapy were enrolled at 19 multiple sclerosis centres in the USA. Participants were randomly assigned (1:1 by site) with an interactive response technology system to either continue or discontinue disease-modifying therapy. Relapse assessors and MRI readers were masked to patient assignment; patients and treating investigators were not masked. The primary outcome was percentage of individuals with a new disease event, defined as a multiple sclerosis relapse or a new or expanding T2 brain MRI lesion, over 2 years. We assessed whether discontinuation of disease-modifying therapy was non-inferior to continuation using a non-inferiority, intention-to-treat analysis of all randomly assigned patients, with a predefined non-inferiority margin of 8%. This trial is registered at ClinicalTrials.gov, NCT03073603, and is completed. FINDINGS: 259 participants were enrolled between May 22, 2017, and Feb 3, 2020; 128 (49%) were assigned to the continue group and 131 (51%) to the discontinue group. Five participants were lost to follow-up (continue n=1, discontinue n=4). Six (4·7%) of 128 participants in the continue group and 16 (12·2%) of 131 in the discontinue group had a relapse or a new or expanding brain MRI lesion within 2 years. The difference in event rates was 7·5 percentage points (95% CI 0·6-15·0). Similar numbers of participants had adverse events (109 [85%] of 128 vs 104 [79%] of 131) and serious adverse events (20 [16%] vs 18 [14%]), but more adverse events (422 vs 347) and serious adverse events (40 vs 30) occurred in the discontinue group. The most common adverse events were upper respiratory infections (20 events in 19 [15%] participants in the continue group and 37 events in 30 [23%] participants in the discontinue group). Three participants in the continue group and four in the discontinue group had treatment-related adverse events, of which one in each group was a serious adverse event (multiple sclerosis relapse requiring admission to hospital). One participant in the continue group and two in the discontinue group died; no deaths were deemed to be related to treatment. INTERPRETATION: We were unable to reject the null hypothesis and could not conclude whether disease-modifying therapy discontinuation is non-inferior to continuation in patients older than 55 years with multiple sclerosis and no recent relapse or new MRI activity. Discontinuation of disease-modifying therapy might be a reasonable option in patients older than 55 years who have stable multiple sclerosis, but might be associated with a small increased risk of new MRI activity. FUNDING: Patient-Centered Outcomes Research Institute and the National Multiple Sclerosis Society.

Treatment of relapsing-remitting multiple sclerosis: current approaches and unmet needs.

PURPOSE OF REVIEW: The aim of this review is to summarize unmet needs for patients with multiple sclerosis (MS). It is important to understand the current status of these patients and both the benefits and limitations of the most commonly used MS treatments as new medications with the potential to simplify therapy and improve outcomes may soon be available. RECENT FINDINGS: Current treatments for MS decrease the frequency of relapses and slow progressive disability. However, nearly all of these medications require frequent administration, and some patients also experience side effects. In some patients, adherence to MS treatment may be less than optimal. This may be associated with increased risk for relapses and hospitalizations and higher cost of care. SUMMARY: Healthcare providers involved in the treatment of MS must be aware of the unmet needs of their patients and intervene as needed to improve adherence and/or modify treatment regimens to optimize outcomes.

Pre-specified subgroup analyses of a placebo-controlled phase III trial (TEMSO) of oral teriflunomide in relapsing multiple sclerosis.

BACKGROUND: The Teriflunomide Multiple Sclerosis Oral (TEMSO) trial, a randomized, double-blind, placebo-controlled phase III study, demonstrated that teriflunomide significantly reduced annualized relapse rate (ARR), disease progression and magnetic resonance imaging (MRI) activity, with a favorable safety profile in relapsing multiple sclerosis (RMS) patients. OBJECTIVE: The purpose of this study was to report the effects of teriflunomide on ARR and disability progression in pre-specified subgroups. METHODS: RMS patients (n=1088) were randomized to placebo or teriflunomide, 7 mg or 14 mg, once daily, for 108 weeks. Subgroup analyses were performed for ARR and disability progression by baseline demographics (gender, race, age), disease characteristics (Expanded Disability Status Scale (EDSS) strata, relapse history, multiple sclerosis (MS) subtype), MRI parameters (gadolinium-enhancing lesions, total lesion volume) and prior use of MS drugs. A generalized estimating equation method and Cox regression model were used to assess consistency of the treatment effect across subgroups, utilizing a treatment-by-subgroup interaction test for each factor separately. RESULTS: Reductions in ARR and disability progression were consistent across subgroups in favor of teriflunomide, with no treatment-by-subgroup interaction test reaching statistical significance. CONCLUSION: The positive effects of teriflunomide were demonstrated consistently across subgroups in TEMSO.

Sex-Dependent Alterations in the mRNA Expression of Enzymes Involved in Dopamine Synthesis and Breakdown After Methamphetamine Self-Administration.

Sex differences have been reported in methamphetamine (METH) use disorder in humans and in animal models of METH exposure. Specifically, animals that self-administer METH show sex-related dissimilarities in dopamine (DA) metabolism. To better understand the molecular bases for the differences in DA metabolism, we measured the levels of mRNAs of enzymes that catalyze DA synthesis and breakdown in the prefrontal cortex (PFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and hippocampus (HIP) of rats that had self-administered METH. There were significant sex differences in control rats, with males having higher basal levels of Th in the PFC and dSTR, Ddc in the NAc, and MaoB in the HIP. In contrast, female controls showed higher basal levels of Comt in the HIP. Male and female METH SA rats also showed some distinct responses to the drug. Specifically, female METH rats exhibited increased expression of Ddc and MaoB, whereas male METH animals showed higher levels of Comt mRNA in the PFC compared to their respective controls. In the NAc, male METH rats displayed decreased Th and Ddc mRNA levels. Together, our results identified sex-dependent and region-specific changes in the mRNA expression of several enzymes involved in DA synthesis and breakdown in response to METH SA, with the majority of differences being observed in the mesocorticolimbic dopaminergic system. These findings are of significant translational importance providing further support for the inclusion of sex as an important variable when planning and evaluating therapeutic interventions against METH use disorder in human clinical studies.