3,4‐diaminopyridine base effectively treats the weakness of Lambert‐Eaton myasthenia

Introduction: 3,4‐diaminopyridine has been used to treat Lambert‐Eaton myasthenia (LEM) for 30 years despite the lack of conclusive evidence of efficacy. Methods: We conducted a randomized double‐blind placebo‐controlled withdrawal study in patients with LEM who had been on stable regimens of 3,4‐diaminopyridine base (3,4‐DAP) for ≥ 3 months. The primary efficacy endpoint was >30% deterioration in triple timed up‐and‐go (3TUG) times during tapered drug withdrawal. The secondary endpoint was self‐assessment of LEM–related weakness (W‐SAS). Results: Thirty‐two participants were randomized to continuous 3,4‐DAP or placebo groups. None of the 14 participants who received continuous 3,4‐DAP had > 30% deterioration in 3TUG time versus 72% of the 18 who tapered to placebo (P < 0.0001). W‐SAS similarly demonstrated an advantage for continuous treatment over placebo (P < 0.0001). Requirement for rescue and adverse events were more common in the placebo group. Discussion: This trial provides significant evidence of efficacy of 3,4‐DAP in the maintenance of strength in LEM. Muscle Nerve 57 : 561–568, 2018     

Post-exercise exhaustion in Lambert–Eaton myasthenic syndrome

ObjectivesTo study post-exercise exhaustion by decrement (PEE-D) systematically in 24 repetitive nerve stimulation (RNS) tests in 14 patients with Lambert–Eaton myasthenic syndrome (LEMS).MethodsIn the abductor digiti quinti muscle, the compound muscle action potential (CMAP) amplitude and 3 Hz responses for 2 s were obtained with the supramaximal stimulation at rest, immediately after (PE0), 30 s after (PE30s), and at 1, 2, 3, and 4 m after 10-s exercise.ResultsThere was a 377% increment in the CMAP amplitude at PE0 and a mild increment (+26%) at PE30s. A transient but significant improvement (−22%) in the decremental response was observed at PE0, and a gradual worsening of decrement in subsequent tests, with the worst decrement noted (−50%) at PE2m.ConclusionPEE-D was found 2 m after exercise in LEMS.SignificancePEE-D may be physiologically closest to the reversible myasthenic fatigue after exercise observed in LEMS patients.     

Myasthenia gravis Lambert‐Eaton overlap syndrome

Introduction: To assess whether a myasthenia gravis (MG) Lambert‐Eaton overlap syndrome (MLOS) exists. Methods: Case reports that met the universally accepted diagnostic criteria for MG and Lambert‐Eaton myasthenic syndrome (LEMS) were sought through a PubMed search. Fifty‐five possible cases of MLOS were identified. Results: Thirty‐nine cases met the diagnostic criteria for MG and LEMS. Analysis of clinical features showed that these patients have common MG and LEMS symptoms: oculo‐bulbar paresis and good response to anti‐cholinesterase for MG and limb weakness and decreased or absent reflexes for LEMS. All had the classical LEMS pattern in the repetitive nerve stimulation test: low compound muscle action potential amplitude and incremental response > 60% with brief exercise or at high rate of stimulation. Eight patients had combined positive acetylcholine receptor antibody (AChR‐ab) or muscle‐specific kinase‐ab and voltage‐gated calcium channel‐ ab tests. Conclusions: A myasthenia gravis Lambert‐Eaton overlap syndrome (MLOS) does exist. Muscle Nerve 53 : 20–26, 2016     

A randomized trial of 3,4-diaminopyridine in Lambert-Eaton myasthenic syndrome

OBJECTIVES: The authors report the results of a prospective, placebo-controlled, randomized study to evaluate the effectiveness of 3,4-diaminopyridine (DAP) in patients with Lambert-Eaton myasthenic syndrome (LEMS) and to determine the acute and long-term side effects of DAP. METHODS: Twenty-six patients with LEMS completed a two-arm parallel treatment protocol in which DAP, 20 mg three times daily, or placebo was given blindly for 6 days, and a quantitative examination of muscle strength (the quantitative myasthenia gravis [QMG] score) was used as the primary measure of efficacy. After the blinded study, patients were given open-label DAP and monitored for side effects as long as there was symptomatic improvement. RESULTS: Twelve patients took DAP, and 14 took placebo. There was no difference in the age of LEMS onset, gender distribution, incidence of lung cancer, or baseline muscle strength between the patients who were randomly assigned to receive placebo and those randomly assigned to DAP. Statistical analysis using the Wilcoxon's rank sum test demonstrated that patients who received DAP had a significantly greater improvement in the QMG score and in the summated amplitude of compound muscle action potentials recorded from three sentinel limb muscles. All but one LEMS patient had significant symptomatic improvement from subsequent open-label DAP. Side effects of DAP were negligible, consisting of perioral and digital paresthesia. Laboratory measurements demonstrated no evidence of toxicity affecting liver, renal, hematologic, endocrinologic, encephalographic, or electrocardiologic function acutely or after 6 months of open-label DAP. CONCLUSIONS: This study corroborates previous studies and many years of clinical experience showing that DAP is an effective and safe treatment for LEMS.     

A randomized,double‐blind,placebo‐controlled phase II study of eculizumab in patients with refractory generalized myasthenia gravis

Introduction: Complement activation at the neuromuscular junction is a primary cause of acetylcholine receptor loss and failure of neuromuscular transmission in myasthenia gravis (MG). Eculizumab, a humanized monoclonal antibody, blocks the formation of terminal complement complex by specifically preventing the enzymatic cleavage of complement 5 (C5). Methods: This study was a randomized, double‐blind, placebo‐controlled, crossover trial involving 14 patients with severe, refractory generalized MG (gMG). Results: Six of 7 patients treated with eculizumab for 16 weeks (86%) achieved the primary endpoint of a 3‐point reduction in the quantitative myasthenia gravis (QMG) score. Examining both treatment periods, the overall change in mean QMG total score was significantly different between eculizumab and placebo (P = 0.0144). After assessing data obtained from all visits, the overall change in mean QMG total score from baseline was found to be significantly different between eculizumab and placebo (P < 0.0001). Eculizumab was well tolerated. Conclusion: The data suggest that eculizumab may have a role in treating severe, refractory MG. Muscle Nerve, 2013     

Repetitive nerve stimulation studies in the Lambert–Eaton myasthenic syndrome

We compared changes in amplitude and area of surface recorded compound motor action potentials (CMAPs) during 20-Hz repetitive nerve stimulation and after maximum voluntary contraction in patients with the Lambert–Eaton myasthenic syndrome (LEMS), myasthenia gravis (MG), and normal controls. There was greater potentiation of CMAP amplitude after voluntary contraction than during 20-Hz stimulation in 10 of 14 LEMS patients; CMAP area increased more after exercise than during 20-Hz stimulation in all LEMS patients. Although abnormal potentiation of CMAP area and amplitude was seen in equal numbers of LEMS patients, more LEMS patients demonstrated a greater than 100% potentiation of CMAP area than of CMAP amplitude. We conclude that maximum voluntary contraction is preferable to brief 20-Hz RNS to demonstrate potentiation in LEMS because it is at least as sensitive and is less painful. Measurement of CMAP area in LEMS patients is not better than measuring the change in CMAP amplitude in demonstrating abnormal potentiation. Testing of a single hand muscle for potentiation in LEMS does not demonstrate abnormal potentiation in all LEMS patients. © 1994 John Wiley & Sons, Inc.     

Electrophysiological differences in seropositive and seronegative Lambert-Eaton myasthenic syndrome

In order to determine whether there is any difference between voltage-gated calcium-channel antibody (VGCC-Ab)-positive and -negative groups in Lambert-Eaton myasthenic syndrome (LEMS), we compared the clinical and electrophysiological features between 13 patients with VGCC-Ab and 6 VGCC-Ab-negative patients. No obvious difference was observed in the various clinical features or findings on single-fiber electromyography between seropositive and seronegative cases. In seropositive cases, the compound muscle action potential (CMAP) amplitude was lower but the increment on post-exercise facilitation (PEF) and high-rate stimulation (HRS) was significantly higher than in the seronegative group, indicating that the repetitive nerve stimulation (RNS) test in the seropositive group is more typical of LEMS and more severe. A 100% increment as the diagnostic criterion in the routine RNS test was satisfied in all seropositive cases but in only three seronegative cases, whereas a 60% increment as the diagnostic criterion was found in all seronegative cases. The classic triad (low CMAP amplitude, decrement at low rate of stimulation, and increment at PEF or HRS) of RNS is rare, adding to the difficulty in diagnosing LEMS in the seronegative group, and making a 60% increment criterion more critical for the diagnosis of this disorder.     

Practical aspects of 3,4-diaminopyridine treatment of the Lambert-Eaton myasthenic syndrome

3,4-Diaminopyridine (3,4-DAP) given alone or combined with pyridostigmine is the recommended basic therapy in the Lambert-Eaton myasthenic syndrome (LEMS). We present and exemplify our routine test protocol for monitoring drug introduction and treatment regimen of cholinergic drugs in LEMS. The individual drug responses vary and no recommended standard doses exist. Routine electrophysiological repetitive nerve stimulation studies recording amplitude of initial compound muscle action potential (CMAP) in thenar muscles correlate excellently with clinical myasthenic muscle power tests in clinically affected muscle groups. Therefore repetitive clinical muscle power tests, that often are complicated by painful myalgia and activation potentiation, can be replaced by recordings of CMAP in the introduction and clinical follow up of cholinergic drug treatment in LEMS. Also, adverse effects and other treatment problems from the experience of continuous treatment of 19 LEMS patients with 3,4-DAP for up to 10 years are presented.     

HTLV‐1–associated myelopathy/tropical spastic paraparesis and peripheral neuropathy following live‐donor renal transplantation

Introduction: Our aim in this study was to provide an updated literature review of electrodiagnostic testing in myasthenia gravis and Lambert–Eaton myasthenic syndrome. Methods: A systematic review of the recent literature was performed using the following key words: myasthenia gravis (MG); Lambert–Eaton myasthenic syndrome (LEMS); electromyography (EMG); repetitive nerve stimulation (RNS); single‐fiber electromyography (SFEMG); nerve conduction study; and normative values. Results: Several articles supported testing of facial, bulbar, and respiratory muscles in the diagnosis of neuromuscular junction (NMJ) disorders, including muscle‐specific kinase antibody (MuSK)‐seropositive MG. Several articles supported use of concentric needle EMG as an alternative to SFEMG jitter in disorders of neuromuscular transmission. A limited number of articles addressed measurement of area (vs. amplitude) decrement in RNS and decreasing the threshold of post‐exercise facilitation. Conclusions: Electrodiagnostic testing continues to be useful for diagnosis of MG and LEMS, although the quality of the evidence is not great. This literature review summarizes RNS and jitter measurement of facial and respiratory muscles and use of concentric needle EMG for SFEMG. Muscle Nerve 52:455–462, 2015     

Effect of 3,4-diaminopyridine on the time course of decay of compound muscle action potential augmentation in the Lambert–Eaton myasthenic syndrome

3,4-Diaminopyridine (3,4-DAP) is known to be beneficial in the symptomatic treatment of the Lambert–Eaton myasthenic syndrome (LEMS). The effects of 3,4-DAP on the decay of postexercise augmentation were observed in 6 patients with LEMS. After 10 s maximal voluntary contraction, the amplitude of the compound muscle action potential (CMAP) recorded from abductor digiti minimi decayed exponentially after an initial rise. The rate of decay in CMAP amplitude was increased after treatment with 3,4-DAP, suggesting that this drug has an effect on the efflux of calcium ions from the presynaptic nerve terminal. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1196–1198, 1998.     

Electrophysiologic correlations with clinical outcomes in CIDP

Data are lacking on correlations between changes in nerve conduction (NC) studies and treatment response in chronic inflammatory demyelinating polyneuropathy (CIDP). This report examined data from a randomized, double‐blind trial of immune globulin intravenous, 10% caprylate/chromatography purified (IGIV‐C [Gamunex]; n = 59) versus placebo (n = 58) every 3 weeks for up to 24 weeks in CIDP. Motor NC results and clinical measures were assessed at baseline and endpoint/week 24. Improvement from baseline in adjusted inflammatory neuropathy cause and treatment score correlated with improvement in proximally evoked compound muscle action potential (CMAP) amplitudes (r = ?0.53; P < 0.001) of all nerves tested and with improvement in CMAP amplitude of the most severely affected motor nerve (r = ?0.36; P < 0.001). Correlations were observed between improvement in averaged CMAP amplitudes and dominant‐hand grip strength (r = 0.44; P < 0.001) and Medical Research Council sum score (r = 0.38; P < 0.001). Overall, the change in electrophysiologic measures of NC in CIDP correlated with clinical response to treatment. Muscle Nerve, 2010     

Single‐fiber EMG and clinical correlation in Lambert‐Eaton myasthenic syndrome

Objectives: We analyzed 82 single‐fiber EMG (SFEMG) tests in the extensor digitorum communis muscle in 30 Lambert‐Eaton myasthenic syndrome (LEMS) patients to study the relationship between electrodiagnostic findings and clinical severity. Methods: The repetitive nerve stimulation test was performed in the abductor digiti quinti and flexor carpi ulnaris muscles. SFEMG was performed in the extensor digitorum communis muscle using the conventional method. Results: Fiber density was normal in all patients. Jitter was abnormal in all patients at the first evaluation regardless of clinical severity. The jitter was increasingly abnormal with worsening disease severity. Mean MCD correlated well with clinical and electrophysiological severity. In 5 potential pairs in 3 patients, MCD analysis in relation to firing rate showed improvement with increasing firing rates, which is consistent with presynaptic neuromuscular transmission disorders. Conclusions: In all LEMS studies, SFEMG was abnormal on the first evaluation. The mean MCD correlated well with clinical and electrophysiological disease severity on the repetitive nerve stimulation test. Muscle Nerve 47: 664–667, 2013     

Low-dose guanidine and pyridostigmine: relatively safe and effective long-term symptomatic therapy in Lambert-Eaton myasthenic syndrome

Guanidine hydrochloride is known to be highly effective in the symptomatic treatment of the Lambert-Eaton myasthenic syndrome (LEMS). However, because of its potentially dangerous side reactions of hematologic abnormalities and renal insufficiency, 3,4-diaminopyridine, which is not readily available in the United States, is recommended as the preferred drug for LEMS. We used low-dose guanidine and pyridostigmine combination therapy in 9 patients with LEMS and analyzed its long-term safety and effectiveness. In all patients, a liberal amount of pyridostigmine was used, while daily guanidine dose was kept below 1000 mg a day, and guanidine was given between pyridostigmine dosings. This combination therapy was used for 3–102 months (mean: 34.1 months) and improved clinical status in all patients. Although guanidine had to be discontinued due to severe gastrointestinal symptoms in 3 cases, no serious side reactions such as bone marrow suppressions or signs of renal insufficiency developed in any case. Thus, we conclude that low-dose guanidine therapy is relatively safe and effective for long-term symptomatic treatment of LEMS when it is combined with pyridostigmine. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20:1146–1152, 1997     

Stratifying disease stages with different progression rates determined by electrophysiological tests in patients with amyotrophic lateral sclerosis

By determining the usefulness of motor unit number estimate (MUNE) and compound muscle action potential (CMAP) amplitude in patients with amyotrophic lateral sclerosis (ALS), we tried to find an effective way to stratify the disease stages. In all, 112 consecutive ALS patients were enrolled, among whom 73 were elicited in a longitudinal study. MUNE by the standard incremental technique, the average CMAP amplitude, total Medical Research Council (MRC) score, ALS‐functional rating score (ALS‐FRS), Appel ALS rating scale (AARS), and forced vital capacity (FVC) were performed at baseline and months 3, 6, and 12 after study entry. We found MUNE correlated with CMAP amplitude (P < 0.01) as well as MRC score (P < 0.01) in regionally concordant distal muscles. Both MUNE and CMAP amplitude correlated significantly with ALS‐FRS (P < 0.05) and AARS (P < 0.01). A MUNE decrease was observed at months 3, 6, and 12 compared with baseline, and the rate of change at month 3 was 50.47%. The decrease in MUNE over the first 3 months was significantly greater than other measurements. We arbitrarily divided the patients into three stages: (1) rapid progression: the rate of change of MUNE and CMAP amplitude during the first 3 months exceeded 50%; (2) moderate progression: the rate of change of MUNE was greater than 50% but CMAP amplitude was less than 50%; (3) slow progression: the rate of change of both MUNE and CMAP amplitude were less than 50%. Comparing the rate of ALS‐FRS descent per year using one‐way ANOVA showed a significant difference among the three groups (P < 0.01). Muscle Nerve 39: 304–309, 2009     

Minimal clinically important difference in myasthenia gravis: Outcomes from a randomized trial

Introduction: The minimal clinically important difference (MCID) is the smallest outcome change that has clinical significance. Its use has not been established in the study of myasthenia gravis (MG). Methods: Patients from a published intravenous immunoglobulin (IVIg) vs. placebo study were studied. One anchor‐based and 3 distribution‐based techniques were used to identify quantitative myasthenia gravis score (QMGS), repetitive nerve stimulation (RNS), and single‐fiber electromyography (SFEMG) MCID cut‐offs. Patients with a change‐score exceeding MCID cut‐offs were compared. Results: MCID cut‐offs were below a QMGS change of 3.0. Anchor‐based and 1 × SEM cut‐offs showed 58.3% vs. 30.7% responders (P = 0.017), ½ SD 54.2% vs. 19.2% responders (P = 0.018), and effect size 0.519 vs. 0.164 (P = 0.011) in IVIg vs. placebo. Anchor‐based (P = 0.73) and effect‐size (P = 0.41) MCID cut‐offs did not show a difference between IVIg and placebo. MCID methods did not produce meaningful RNS cut‐offs. Conclusions: QMGS MCID values provide clinically relevant information and are recommended in MG trials. MCID analysis shows that improvement in MG patients treated with IVIg reflects clinically meaningful changes. Muscle Nerve 49 : 661–665, 2014     

Rotigotine effects on early morning motor function and sleep in Parkinson's disease: A double‐blind,randomized, placebo‐controlled study (RECOVER)

In a multinational, double‐blind, placebo‐controlled trial (NCT00474058), 287 subjects with Parkinson's disease (PD) and unsatisfactory early‐morning motor symptom control were randomized 2:1 to receive rotigotine (2–16 mg/24 hr [n = 190]) or placebo (n = 97). Treatment was titrated to optimal dose over 1–8 weeks with subsequent dose maintenance for 4 weeks. Early‐morning motor function and nocturnal sleep disturbance were assessed as coprimary efficacy endpoints using the Unified Parkinson's Disease Rating Scale (UPDRS) Part III (Motor Examination) measured in the early morning prior to any medication intake and the modified Parkinson's Disease Sleep Scale (PDSS‐2) (mean change from baseline to end of maintenance [EOM], last observation carried forward). At EOM, mean UPDRS Part III score had decreased by ?7.0 points with rotigotine (from a baseline of 29.6 [standard deviation (SD) 12.3] and by ?3.9 points with placebo (baseline 32.0 [13.3]). Mean PDSS‐2 total score had decreased by ?5.9 points with rotigotine (from a baseline of 19.3 [SD 9.3]) and by ?1.9 points with placebo (baseline 20.5 [10.4]). This represented a significantly greater improvement with rotigotine compared with placebo on both the UPDRS Part III (treatment difference: ?3.55 [95% confidence interval (CI) ?5.37, ?1.73]; P = 0.0002) and PDSS‐2 (treatment difference: ?4.26 [95% CI ?6.08, ?2.45]; P < 0.0001). The most frequently reported adverse events were nausea (placebo, 9%; rotigotine, 21%), application site reactions (placebo, 4%; rotigotine, 15%), and dizziness (placebo, 6%; rotigotine 10%). Twenty‐four‐hour transdermal delivery of rotigotine to PD patients with early‐morning motor dysfunction resulted in significant benefits in control of both motor function and nocturnal sleep disturbances. © 2010 Movement Disorder Society     

A double‐blind,placebo‐controlled trial of rosiglitazone for clozapine‐induced glucose metabolism impairment in patients with Schizophrenia

Objective: The primary purpose of this 8‐week double‐blind, placebo‐controlled trial of rosiglitazone 4 mg/day was to examine its effect on insulin sensitivity index (SI) and glucose utilization (SG) in clozapine‐treated subjects with schizophrenia with insulin resistance. Method: Eighteen subjects were randomized and accessed with a Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT) at baseline and at week 8 to estimate SG and SI. Results: Controlling for the baseline, comparing the rosiglitazone group with placebo group, there was a non‐significant improvement in SG (0.016 ± 0.006–0.018 ± 0.008, effect size = 0.23, P = 0.05) with a trend of improvement in SI in the rosiglitazone group (4.6 ± 2.8–7.8 ± 6.7, effect size = 0.18, P = 0.08). There was a significant reduction in small low‐density lipoprotein cholesterol (LDL‐C) particle number (987 ± 443–694 ± 415, effect size = 0.30, P = 0.04). Conclusion: Rosiglitazone may have a role in addressing insulin resistance and lipid abnormalities associated with clozapine.     

Proteasome inhibitors for malignancy‐related lambert‐eaton myasthenic syndrome

Lambert‐Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by autoantibodies against presynaptic voltage‐gated calcium channels that impair neuromuscular transmission. Malignancies, especially small cell lung cancer (SCLC), have been associated with LEMS and account for approximately 60% of cases, making malignancy management a central step in LEMS therapy. In addition, immunosuppressive therapy is also recommended for symptomatic control. Interestingly, both pathological and epidemiological data suggest that the autoimmune response can inhibit progression of tumors in malignancy‐associated LEMS. Thus, conventional broad‐spectrum immunosuppressants may not be effective agents for treatment of LEMS, especially in those with malignancy‐associated LEMS. Recent preclinical and clinical studies have indicated that proteasome inhibitors can eliminate antibody‐producing cells efficiently, block dendritic cell maturation, and have anti‐tumor activity. We hypothesize that proteasome inhibitors may be promising agents for treatment of malignancy‐related LEMS. Muscle Nerve 49 :325–328, 2014     

Distribution of electrophysiological abnormality in Lambert-Eaton myasthenic syndrome

OBJECTIVE—Toassess the distribution of electrophysiological abnormality inLambert-Eaton myasthenic syndrome (LEMS) to identify the most sensitivemuscle to use in routine examination.
METHODS—Surfacerecorded compound muscle action potential (CMAP) amplitudes were madefrom abductor digiti minimi, abductor pollicis brevis, anconeus, bicepsbrachii, and trapezius in 10 patients with LEMS. The effect of3,4-diaminopyridine (3,4-DAP) was recorded in each muscle in ninepatients. CMAP amplitudes were measured at rest and immediately after10 seconds maximal voluntary contraction in each muscle. Values werecompared with results obtained from 12 healthy controls.
RESULTS—Resting CMAPamplitudes were reduced in at least one muscle in all patients comparedwith controls, most markedly in abductor digiti minimi and anconeus.The administration of 3,4-DAP resulted in significantly improvedresting CMAP amplitudes in trapezius only. After maximal voluntarymuscle contraction, characteristic increments in CMAP amplitude of over100% above resting values were seen in abductor digiti minimi andabductor pollicis brevis in seven patients, anconeus and biceps brachiiin five patients. No patient had this level of increment in trapezius.
CONCLUSION—Despitepredominantly proximal limb weakness seen clinically in patientswith LEMS, the most sensitive muscles for detecting characteristicelectrophysiological abnormalities of low resting CMAP amplitude andincrement of over 100% after 10 seconds maximal voluntarycontraction are abductor digiti minimi, abductor pollicis brevis, and anconeus.

     

Clinical efficacy of istradefylline (KW‐6002) in Parkinson's disease: A randomized,controlled study

The objectives of this study were to evaluate the efficacy of istradefylline at an oral dose of 20 mg or 40 mg once daily for 12 weeks in Parkinson's disease (PD) patients with motor complications on levodopa therapy based on the change in the daily OFF time compared with placebo and to assess the safety at these doses. A total of 363 subjects were randomly assigned to receive 20 mg/day istradefylline (n = 119), 40 mg/day istradefylline (n = 125), or placebo (n = 119). The primary outcome variable was the change from baseline at endpoint in daily OFF time based on patients' ON/OFF diaries. At endpoint, the daily OFF time reduced from baseline by 1.31 hours for 20 mg/day istradefylline (P = 0.013 as compared to the placebo), 1.58 hours for 40 mg/day istradefylline (P < 0.001), and 0.66 hours for placebo; istradefylline significantly reduced the daily OFF time compared with placebo. The UPDRS Part III subscale score (ON state) reduced by 5.7 at endpoint in both istradefylline groups and 3.7 in the placebo group (P = 0.006 for 20 mg/day and P = 0.006 for 40 mg/day group as compared with placebo). The most commonly reported drug‐related treatment emergent adverse event (TEAE) was dyskinesia, which occurred in 2.5% (3/119) of subjects receiving placebo, 8.5% (10/118) receiving 20 mg/day istradefylline, and 6.4% (8/125) receiving 40 mg/day istradefylline. We conclude that istradefylline at 20 mg and 40 mg once daily is effective in relieving wearing‐off fluctuations of PD patients. In addition, istradefylline was well tolerated at both doses. © 2010 Movement Disorder Society