Robotic stereotactic ablative radiotherapy for renal cell carcinoma in patients with impaired renal function.

BACKGROUND: Robotic stereotactic ablative radiotherapy (SABR) is currently under investigation as a noninvasive treatment option for patients with renal cell carcinoma (RCC). For radiation therapy of RCC, tumor motion and the need for high ablative doses while preserving the remaining renal parenchyma is a challenge. We aimed to analyze the safety and efficacy of robotic radiosurgery in RCC in a specific difficult subgroup of patients with impaired renal function. METHODS: We retrospectively identified all patients with RCC, treated with robotic SABR and motion compensation in our institution between 2012 and 2017. Either single fraction SABR of 24 or 25 Gy or 3 fractions of 12 Gy prescribed to the 70% isodose line was applied. Local control, overall survival, radiation side effects were evaluated together with renal function and tumor motion. RESULTS: We analyzed data of 13 lesions treated in 10 patients with clear cell RCC and a mean age of 70.5 ± 13.6 years (range: 48-87). Prior to SABR, 8 patients underwent previous complete and/or partial nephrectomy, 7 patients presented with chronic kidney disease ≥ stage 3. The median of minimum, mean and maximum planning target volume doses were 23.2, 29.5 and 35.0 Gy for single fraction and 24.4, 42.5 and 51.4 Gy for the three fractions regime. Persistent local control by robotic SABR was achieved in 9 out of 10 patients (92.3% of all lesions) within a median follow-up period of 27 month (range: 15-54). One patient underwent nephrectomy due to progressive disease and sufficient renal function of the contralateral kidney. Renal function remained stable with a mean estimated glomerular filtration rate (eGFR) of 51.3 ± 19.7 ml/min at baseline and 51.6 ± 25.8 ml/min at follow-up. The largest respiratory-induced tumor motion was seen in superior-inferior direction, compensated by the CyberKnife with mean targeting errors of maximal 2.2 mm. CONCLUSIONS: Robotic SABR is technically feasible for the treatment of RCC in preexisting kidney disease with good local tumor control at about 2 years follow-up. Robotic SABR with motion tracking offers a valid treatment option for patients, who are at increased risk for progression to end-stage renal disease due to partial nephrectomy or ablative techniques.

Targeted next-generation sequencing identifies molecular subgroups in squamous cell carcinoma of the head and neck with distinct outcome after concurrent chemoradiation.

BACKGROUND: Based on epidemiological (HPV status, smoking habits) and clinical risk factors (T/N stage), three subgroups of patients suffering from locally advanced oropharyngeal carcinoma with significantly different outcome after concurrent chemoradiation (cCRTX) can be distinguished. Mutational profiling by targeted next-generation sequencing (NGS) might further improve risk stratification. PATIENTS AND METHODS: Patients with stage IV squamous cell carcinoma of the oropharynx and hypopharynx who had been enrolled in a randomized phase III trial (ARO-0401) comparing two regimens of cCRTX and from whom archival tumor specimens were available were included. The HPV status was determined by p16 immunostaining and detection of HPV DNA. Targeted NGS covering 45 genes frequently altered in squamous cell carcinoma of the head and neck (SCCHN) was applied for detection of non-synonymous somatic and germline mutations. Interference of mutational profiles with cCRTX efficacy was determined. RESULTS: The prognostic value of the 'Ang' risk model could be confirmed in the total biomarker study cohort (N = 175) as well as the patient subgroup for which mutational profiles could be established (N = 97). Mutations in genes involved in phosphoinositide 3-kinase (PI3K), receptor tyrosine kinase (RTK), and p53 signaling pathways were significantly enriched in the low- (N = 7), intermediate- (N = 20), and high-risk group (N = 70), respectively. Mutations in TP53 identified a subgroup of high-risk patients with dismal outcome after cCRTX. No prognostic relevance was observed for mutations in PI3K and RTK signaling pathways in the low- and intermediate-risk groups, respectively. Mutated NOTCH1 and two functional KDR germline variants (rs2305948, rs1870377) were associated with improved outcome in all risk groups. All genetic markers (TP53, NOTCH1, KDR) remained independent prognosticators of OS in the multivariate model. CONCLUSION: A potential of targeted NGS for risk classification of SCCHN cases beyond HPV status and clinical factors was demonstrated.

Detection of circulating tumor cells for prediction of recurrence after adjuvant chemoradiation in locally advanced squamous cell carcinoma of the head and neck.

BACKGROUND: The prognostic role of persistence of circulating tumor cells (CTC) after upfront tumor surgery for outcome of adjuvant (chemo)radiation in locally advanced squamous cell carcinoma of the head and neck (LASCCHN) was evaluated. PATIENTS AND METHODS: In this prospective study, peripheral blood samples from 144 patients with LASCCHN presenting after tumor resection for adjuvant treatment were analyzed for CTC. Their detection was correlated with tumor site, clinical risk factors, disease-free (DFS) and overall survival (OS). RESULTS: CTC were detected in 42 of 144 patients (29%). CTC detection was higher in cases with nodal involvement and in carcinomas located at the tonsil or base of tongue but was not influenced by age, smoking history, T stage, extracapsular lymph node extension, surgical margins or the human papillomavirus status. Overall, the presence of CTC was not predictive for OS or DFS. However, while in oropharyngeal carcinomas (OPC, n = 63), the detection of CTC was associated per trend with improved DFS [CTC+ versus CTC- (% of patients without evidence of disease at 2 years): 100% versus 79%; log rank: P = 0.059]; the reverse was observed for carcinomas from other sites (non-OPC, n = 81; CTC+ versus CTC-: 29% versus 75%; P = 0.001). In multivariate analysis, CTC remained an independent prognostic marker for DFS [hazard ratio (HR) 4.3, 95% confidence interval (CI) 1.7-10.9, P = 0.002] and OS (HR 2.7, 95% CI 1.2-6.3, P = 0.016) in non-OPC. CONCLUSIONS: Assessment of CTC in non-OPC should prove useful for identification of patients who benefit from treatment intensification. The basis for the good prognostic value of CTC in OPC has to be elucidated in future studies.

Concurrent hyperfractionated accelerated radiotherapy with 5-FU and once weekly cisplatin in locally advanced head and neck cancer. The 10-year results of a prospective phase II trial.

PURPOSE: In this study, the acute toxicity and long-term outcome of a hyperfractionated accelerated chemoradiation regimen with cisplatin/5-fluorouracil (5-FU) in patients with locally advanced squamous cell carcinomas of head and neck were evaluated. PATIENTS AND METHODS: From 2000-2002, 38 patients with stage III (5.3 %) and stage IV (94.7 %) head and neck cancer were enrolled in a phase II study. Patients received hyperfractionated-accelerated radiotherapy with 72 Gy in 15 fractions of 2 Gy followed by 1.4 Gy twice daily with concurrent, continuous infusion 5-FU of 600 mg/m(2) on days 1-5 and 6 cycles of weekly cisplatin (30 mg/m(2)). Acute toxicities (CTCAEv2.0), locoregional control (LRC), metastases-free (MFS), and overall survival (OS) were analyzed and exploratively compared with the ARO 95-06 trial. RESULTS: Median follow-up was 11.4 years (95 % CI 8.6-14.2) and mean dose 71.6 Gy. Of the patients, 82 % had 6 (n = 15) or 5 (n = 16) cycles of cisplatin, 5 and 2 patients received 4 and 3 cycles, respectively. Grade 3 anemia, leukopenia, and thrombocytopenia were observed in 15.8, 15.8, and 2.6 %, respectively. Grade 3 mucositis in 50 %, grade 3 and 4 dysphagia in 55 and 13 %. The 2-, 5-, and 10-year LRC was 65, 53.6, and 48.2 %, the MFS was 77.5, 66.7, and 57.2 % and the OS 59.6, 29.2, and 15 %, respectively. CONCLUSION: Chemoradiation with 5-FU and cisplatin seems feasible and superior in terms of LRC and OS to the ARO 95-06C-HART arm at 2 years. However, this did not persist at the 5- and 10-year follow-ups.

Design and evaluation of a deep learning-based automatic segmentation of maxillary and mandibular substructures using a 3D U-Net.

Background: Current segmentation approaches for radiation treatment planning in head and neck cancer patients (HNCP) typically consider the entire mandible as an organ at risk, whereas segmentation of the maxilla remains uncommon. Accurate risk assessment for osteoradionecrosis (ORN) or implant-based dental rehabilitation after radiation therapy may require a nuanced analysis of dose distribution in specific mandibular and maxillary segments. Manual segmentation is time-consuming and inconsistent, and there is no definition of jaw subsections. Materials and methods: The mandible and maxilla were divided into 12 substructures. The model was developed from 82 computed tomography (CT) scans of HNCP and adopts an encoder-decoder three-dimensional (3D) U-Net structure. The efficiency and accuracy of the automated method were compared against manual segmentation on an additional set of 20 independent CT scans. The evaluation metrics used were the Dice similarity coefficient (DSC), 95% Hausdorff distance (HD95), and surface DSC (sDSC). Results: Automated segmentations were performed in a median of 86 s, compared to manual segmentations, which took a median of 53.5 min. The median DSC per substructure ranged from 0.81 to 0.91, and the median HD95 ranged from 1.61 to 4.22. The number of artifacts did not affect these scores. The maxillary substructures showed lower metrics than the mandibular substructures. Conclusions: The jaw substructure segmentation demonstrated high accuracy, time efficiency, and promising results in CT scans with and without metal artifacts. This novel model could provide further investigation into dose relationships with ORN or dental implant failure in normal tissue complication prediction models.

Oligometastases: the new paradigm and options for radiotherapy. A critical review.

Traditional oncology distinguishes between two separate and incommensurable states in the evolution of solid malignancies: the localized disease, which is curable; and the disseminated status, which is per se palliative. Recently, a huge body of evidence suggests a fundamental change in the understanding of cancer, indicating an intermediate state in the trajectory of solid malignancies: the oligometastatic state. The following review will critically analyse existing hypotheses and facts from the basic sciences and try to contextualize it in regard to the clinical evidence available to date. Consecutively, it will try to draw possible clinical consequences for application of radiotherapy in this specific clinical scenario.

[Radiation therapy in patients with cardiac pacemakers or implantable cardioverter defibrillators. Interdisciplinary safety recommendations]. / Strahlentherapie bei Patienten mit Herzschrittmachern oder implantierbaren Kardioverter-Defibrillatoren. Interdisziplinäre Sicherheitsempfehlungen.

BACKGROUND: With increasing numbers of implanted pacemakers and implantable cardioverter defibrillators (ICD) and a rising incidence of malignant tumors, there is a growing probability of radiation-mediated device dysfunction. The only guidelines for the management of patients with cardiac pacemakers in the case of radiation therapy were published in 1994 and have not been updated since then. Based on the current evidence and modern device technology, the present paper aims to develop contemporary and interdisciplinary safety recommendations for the minimization of patient risk. METHODS AND RESULTS: A systematic literature research was carried out including the most relevant medical electronic databases. The search yielded 147 articles published between 1994 and 2012 of which 45 met the selection criteria and of these studies 34 presented primary data (9 in vitro and 25 in vivo studies). The impact of ionizing radiation varied significantly between implanted devices and ranged from no functional changes to complete loss of function. Important device dysfunctions included changes in sensing capability, altered pacing pulses or rate, changed or disabled tachyarrhythmia ICD therapies, early battery depletion and loss of telemetry. Modern pacemakers and ICDs are more sensitive to radiation than older models. Potentially life-threatening complications were observed after exposure of the pulse generator to comparatively low radiation doses (0.11 Gy). CONCLUSIONS: Practical recommendations for patient management and safety are presented that can be readily adopted by any institution carrying out radiation therapy.

Impact of cranial irradiation and brain tumor location on fertility: a survey.

As survival rates of patients with childhood brain tumors have increased to 75%, treatment related side effects are of particular importance. The present study evaluated questionnaire-based fertility characteristics in cancer survivors treated with irradiation to the hypo-thalamic-pituitary-axis.A nationwide survey was conducted in collaboration with the German Childhood Cancer Registry. Questionnaire and treatment data could be retrieved for 1110 former childhood cancer patients with cranial irradiation and/or chemotherapy.Survivors receiving ≥30 gray vs. 18-29 gray and 0-17 gray to the pituitary gland reported less pregnancies or less with their partners (7.4% vs. 32.8% vs. 12.4%; p<0.001), were more often infertile (40% vs. 9.4% vs. 12.5%; p<0.001) and the female participants, had a higher frequency of permanent amenorrhea (16.7% vs. 1.7% vs. 0%; p<0.001).Irradiation of the pituitary gland ≥ 30 gray seemed to be associated with less pregnancies and increased permanent amenorrhea in women. Future studies need to be conducted to confirm these results. Increased knowledge of treatment related side effects might help brain tumor patients to improve their family planning if necessary by gonadotropine replacement.

The presence of circulating tumor cells (CTCs) correlates with lymph node metastasis in nonresectable squamous cell carcinoma of the head and neck region (SCCHN).

BACKGROUND: The mechanisms regulating tumor cell dissemination in locally advanced squamous cell carcinoma of the head and neck region (SCCHN) are largely unresolved. We assessed the frequency of circulating tumor cells (CTCs), their association with clinicopathologic parameters and their kinetics during radiochemotherapy. PATIENTS AND METHODS: Peripheral blood samples from 42 patients with locally advanced SCCHN were included. CTCs were detected using flow cytometric analysis of CD45-epithelial cell adhesion molecule+cytokeratin+ cells and results were validated by nested RT-PCR analysis of circulating epidermal growth factor receptor transcripts. The association between the presence of CTCs and T stage, tumor volume, N stage and human papillomavirus status was evaluated. The influence of radiochemotherapy on CTC numbers was determined. RESULTS: CTCs were detected in 18 of 42 SCCHN patients (43%), with a mean ± standard deviation of 1.7 ± 0.9 CTCs per 3.75 ml blood. We observed no significant correlation between the presence of CTCs and T stage or tumor volume. However, a nodal stage of N2b or higher was associated with higher frequency of CTCs. Though concurrent radiochemotherapy reduced their frequency, CTCs persisted during treatment in 20% of cases. CONCLUSIONS: Detection of CTCs correlates with regional metastasis in inoperable SCCHN. Further follow-up is needed to evaluate the prognostic significance of CTC detection, in addition to clinical staging of lymph nodes, for regional or distant recurrence.

Interference of tumour mutational burden with outcome of patients with head and neck cancer treated with definitive chemoradiation: a multicentre retrospective study of the German Cancer Consortium Radiation Oncology Group.

BACKGROUND: Tumour mutational burden (TMB) estimated from whole exome sequencing or comprehensive gene panels has previously been established as predictive factor of response to immune checkpoint inhibitors (ICIs). Its predictive value for the efficacy of concurrent chemoradiation (cCRTX), a potential combination partner of ICI, remains unknown. METHODS: The accuracy of TMB estimation by an in-house 327-gene panel was established in the Cancer Genome Atlas (TCGA) head and neck squamous cell carcinoma (HNSCC) data set. Interference of TMB with outcome after cCRTX was determined in a multicentre cohort of patients with locally advanced HNSCC uniformly treated with cCRTX. Targeted next-generation sequencing was successfully applied in 101 formalin-fixed, paraffin-embedded pretreatment tumour samples. In a subset of cases (n = 40), tumour RNA was used for immune-related gene expression profiling by the nanoString platform. TMB was correlated with TP53 genotype, human papilloma virus (HPV) status, immune expression signatures and survival parameters. Results were validated in the TCGA HNSCC cohort. RESULTS: A high accuracy of TMB estimation by the 327-gene panel was established. High TMB was significantly associated with an increased prevalence of TP53 mutations and immune gene expression patterns unrelated to T cell-inflamed gene expression profiles. Kaplan-Meier analysis revealed significantly reduced overall survival in the patient group with high TMB (hazard ratio for death: 1.79, 95% confidence interval: 1.02-3.14; P = 0.042) which remained significant after correcting for confounding factors in the multivariate model. The prognostic value of TMB was confirmed in the TCGA HNSCC cohort. CONCLUSION: High TMB identifies HNSCC patients with poor outcome after cCRTX who might preferentially benefit from CRTX-ICI combinations.

Contribution of human papilloma virus to the incidence of squamous cell carcinoma of the head and neck in a European population with high smoking prevalence.

BACKGROUND: Increases in incidence of oropharyngeal squamous cell carcinoma (OPSCC) in countries with falling tobacco use have been attributed to a growing role of human papilloma virus (HPV) in the carcinogenesis. Trends of HPV prevalence in populations with persistently high portions of smokers are poorly characterised. PATIENTS AND METHODS: Registry data from East Germany were used to determine incidence trends between 1998 and 2011. Data from patients treated at the Charité University Medicine Berlin between 2004 and 2013 (cohort 1, N=436) were used for estimation of trends in HPV prevalence, smoking and survival. HPV prevalence was prospectively confirmed in cohort 2 (N=213) comprising all primary HNSCC cases at the Charité in 2013. RESULTS: Between 1998 and 2011 incidence of both OPSCC and non-OPSCC increased. An increase in HPV prevalence (% of HPV+ cases in 2004-2006 versus 2012-2013: 27% versus 59%, P=0.0004) accompanied by a moderate decrease in the portion of current smokers was observed in OPSCC but not in non-OPSCC. The change in disease epidemiology in OPSCC was associated with significant improvement in overall survival. Increased HPV prevalence in OPSCC (48%) compared to non-OPSCC (11%) was confirmed in cohort 2. CONCLUSIONS: Despite clear differences to the United States in terms of tobacco use, the increase in OPSCC incidence in a European population was also mainly attributed to HPV, and the HPV status significantly affected prognosis. For clinical trial design it is important to consider the large group of smokers within HPV-induced OPSCC.

Characterization of seven novel mutations in seven patients with GAMT deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive error of creatine synthesis characterized by cerebral creatine deficiency, accumulation of guanidinoacetate, mental retardation, epilepsy and extrapyramidal signs. So far, six mutations have been identified in seven patients. We investigated seven new patients by screening the promoter, 3'UTR, and six exons and exon/intron boundaries using direct sequencing and denaturing gradient gel electrophoresis. The clinical and biochemical phenotype was characterized by scoring the degree of main clinical manifestations and by determination of urinary guanidinoacetate concentrations and of GAMT activity in fibroblasts / lymphoblasts, respectively. We identified 7 novel mutations, including c.64dupG (exon 1; 4/14 alleles); c.59G>C (exon 1; 3/14 alleles); c.491delG (exon 5; 2/14 alleles); c.160G>C (exon 1; 2/14 alleles); and c.152A>C (exon 1; 1/14 alleles); c.526dupG (exon 5; 1/14 alleles); c.521G>A (exon 5; 1/14 alleles), and two polymorphisms c.626C>T (exon 6) and c.459+71G>A (intron 4). Frameshift and missense mutations in exon 1 were prevalent in the 4 patients with the severe phenotype, however a clear genotype-phenotype correlation has not been established in the limited number of patients characterized so far.

Changes of tissue creatine concentrations upon oral supplementation of creatine-monohydrate in various animal species.

Creatine is a nutritional supplement with major application as ergogenic and neuroprotective substrate. Varying supplementation protocols differing in dosage and duration have been applied but systematic studies of total creatine (creatine and phosphocreatine) content in the various organs of interest are lacking. We investigated changes of total creatine concentrations in brain, muscle, heart, kidney, liver, lung and venous/portal plasma of guinea pigs, mice and rats in response to 2-8 weeks oral creatine-monohydrate supplementation (1.3-2 g/kg/d; 1.4-2.8% of dietary intake). Analysis of creatine and phosphocreatine content was performed by high performance liquid chromatography. Total creatine was determined as the sum of creatine and phosphocreatine. Presupplementation total creatine concentrations were high in brain, skeletal and heart muscle (10-22 micromol/g wet weight), and low in liver, kidney and lung (5-8 micromol/g wet weight). During creatine supplementation, the relative increase of total creatine was low (15-55% of presupplementation values) in organs with high presupplementation concentrations, and high (260-500% of presupplementation values) in organs with low presupplementation concentrations. The increase of total creatine concentrations was most pronounced after 4 weeks of supplementation. In muscle, brain, kidney and lungs, an additional increase (p<0.01) was observed between 2-4 and 2-8 weeks of supplementation. Absolute concentrations of phosphocreatine increased, but there was no increase of the relative (percentual) proportion of phosphocreatine (14-45%) during supplementation. Statistical comparison of total creatine concentrations across the species revealed no systematically differences in organ distribution and in time points of supplementation. Results suggest that in organs with low presupplementation creatine levels (liver, kidney), a major determinant of creatine uptake is an extra-intracellular concentration gradient. In organs with high presupplementation total creatine levels like brain, skeletal and heart muscle, the maximum capacity of creatine accumulation is low compared to other organs. A supplementation period of 2 to 4 weeks is necessary for significant augmentation of the creatine pool in these organs.

Pipecolic acid concentrations in brain tissue of nutritionally pyridoxine-deficient rats.

Elevated concentrations of pipecolic acid have been reported in plasma and CSF of patients with pyridoxine-dependent epilepsy, but its molecular background is unclear. To investigate any further association of pyridoxine and pipecolic acid metabolism, we have performed an animal trial and have measured the concentration of pipecolic acid in brain tissue of rats with nutritional pyridoxine deficiency and in control littermates. Concentrations of pyridoxal phosphate were significantly reduced in brain tissue of pyridoxine-deficient rats (p < 0.001), while concentrations of pipecolic acid were not significantly different from the normally nourished control group (p = 0.3). These data indicate that a direct association of pyridoxine and pipecolic acid metabolism is unlikely. We therefore assume that the characteristic elevation of pipecolic acid in pyridoxine-dependent epilepsy could rather be a secondary phenomenon with the primary defect of pyridoxine-dependent epilepsy being located outside the pipecolic acid pathway.

Clinical characteristics and diagnostic clues in inborn errors of creatine metabolism.

Creatine deficiency syndromes are a newly described group of inborn errors of creatine synthesis (arginine:glycine amidinotransferase (AGAT) deficiency and guanidinoaceteate methyltransferase (GAMT) deficiency) and creatine transport (creatine transporter (CRTR) deficiency). The common clinical denominator of creatine deficiency syndromes is mental retardation and epilepsy, suggesting the main involvement of cerebral grey matter (grey matter disease). Patients with GAMT deficiency exhibit a more complex clinical phenotype with dystonic hyperkinetic movement disorder and epilepsy that in some cases is unresponsive to pharmacological treatment. The common biochemical denominator of creatine deficiency syndromes is cerebral creatine deficiency which is demonstrated by in vivo proton magnetic resonance spectroscopy. Measurement of guanidinoacetate in body fluids may discriminate GAMT (high concentration), AGAT (low concentration) and CRTR (normal concentration). Further biochemical characteristics include changes in creatine and creatinine concentrations in body fluids. GAMT and AGAT deficiency are treatable by oral creatine supplementation, while patients with CRTR deficiency do not respond to this type of treatment. Further recognition of patients will be of major importance for the estimation of the frequency, for the understanding of phenotypic variations and for treatment strategies.

Arginine:glycine amidinotransferase deficiency: the third inborn error of creatine metabolism in humans.

Arginine:glycine amidinotransferase (AGAT) catalyzes the first step of creatine synthesis, resulting in the formation of guanidinoacetate, which is a substrate for creatine formation. In two female siblings with mental retardation who had brain creatine deficiency that was reversible by means of oral creatine supplementation and had low urinary guanidinoacetate concentrations, AGAT deficiency was identified as a new genetic defect in creatine metabolism. A homozygous G-A transition at nucleotide position 9297, converting a tryptophan codon (TGG) to a stop codon (TAG) at residue 149 (T149X), resulted in undetectable cDNA, as investigated by reverse-transcription PCR, as well as in undetectable AGAT activity, as investigated radiochemically in cultivated skin fibroblasts and in virus-transformed lymphoblasts of the patients. The parents were heterozygous for the mutant allele, with intermediate residual AGAT activities. Recognition and treatment with oral creatine supplements may prevent neurological sequelae in affected patients.

Effects of oral creatine supplementation in a patient with MELAS phenotype and associated nephropathy.

An 18-year-old male patient with MELAS phenotype and 2 previous episodes of cerebral stroke, recurrent seizures and nephropathy, was treated with creatine monohydrate after the acute onset of psychomental regression and changing states of somnolence and aggressive and agitated behaviour. These symptoms disappeared completely after 4 weeks of treatment with creatine after which the patient regained all his previous mental abilites. Brain (white matter) proton magnetic resonance spectroscopy (chemical shift imaging) performed at 6 and 12 months of treatment showed lactic acid (Lac) accumulation and high creatine (Cr) levels in relation to choline-containing compounds (Cho). Urinary creatinine excretion as an indicator of the muscle and brain creatine pool increased upon short-term (12 days) high-dosage creatine supplementation (20 g per day) while plasma creatinine concentrations as possible indicators both of increasing creatine pool and of renal insufficiency increased during the course (28 months) of low-dosage creatine supplementation (5 g per day). Deterioration of renal function was finally indicated by urea retention and by impairment of renal creatinine clearance. These observations suggest that creatine supplementation may have a neuroprotective effect in patients with MELAS and episodes of acute mental deterioration. Adverse effects of creatine supplementation on renal function must be considered especially in patients with preexisting nephropathy.