Tibialis Anterior Muscle Hernia in a Young Woman

Muscle herniation is defined as a myofascial defect resulting in protruding of the muscle through the fascia covering it. It can present anywhere in the body, the most common is the lower limbs. Tibialis muscle herniation is considered a rare entity with few reported cases. Here, we present the case of a 24-year-old Saudi female patient who complained of swelling and pain in the anterior aspect of the left leg for three months. She underwent surgical repair of the fascia with a good outcome. This case presentation aims to contribute to the literature on myofascial herniation by specifically addressing tibialis anterior herniation of the leg and emphasizing the importance of considering it a differential diagnosis in similar presentations. This report highlights the excellent surgical outcomes and satisfactory results in patients with muscle herniation.

Predicting 5-fluorouracil toxicity: DPD genotype and 5,6-dihydrouracil:uracil ratio

AIM

Decreased DPD activity is a major cause of 5-fluorouracil (5-FU) toxicity, but known reduced-function variants in the DPD gene (DPYD) explain only a part of DPD-related 5-FU toxicities. Here, we evaluated the baseline (pretherapeutic) plasma 5,6-dihydrouracil:uracil (UH2:U) ratio as a marker of DPD activity in the context of DPYD genotypes.

MATERIALS & METHODS

DPYD variants were genotyped and plasma U, UH2 and 5-FU concentrations were determined by liquid chromatography-tandem mass spectrometry in 320 healthy blood donors and 28 cancer patients receiving 5-FU-based chemotherapy.

RESULTS

Baseline UH2:U ratios were strongly correlated with generally low and highly variable U concentrations. Reduced-function DPYD variants were only weakly associated with lower baseline UH2:U ratios. However, the interindividual variability in the UH2:U ratio was reduced and a stronger correlation between ratios and 5-FU exposure was observed in cancer patients during 5-FU administration.

CONCLUSION

These results suggest that the baseline UH2:U plasma ratio in most individuals reflects the nonsaturated state of DPD and is not predictive of decreased DPD activity. It may, however, be highly predictive at increased substrate concentrations, as observed during 5-FU administration.

Translating DPYD genotype into DPD phenotype: using the DPYD gene activity score

The dihydropyrimidine dehydrogenase enzyme (DPD, encoded by the gene DPYD) plays a key role in the metabolism of fluoropyrimidines. DPD deficiency occurs in 4-5% of the population and is associated with severe fluoropyrimidine-related toxicity. Several SNPs in DPYD have been described that lead to absent or reduced enzyme activity, including DPYD*2A, DPYD*13, c.2846A>T and c.1236G>A/haplotype B3. Since these SNPs differ in their effect on DPD enzyme activity, a differentiated dose adaption is recommended. We propose the gene activity score for translating DPYD genotype into phenotype, accounting for differences in functionality of SNPs. This method can be used to standardize individualized fluoropyrimidine dose adjustments, resulting in optimal safety and effectiveness.

Evaluation of 5-fluorouracil pharmacokinetic models and therapeutic drug monitoring in cancer patients

5-fluorouracil (5-FU) remains the cornerstone of all currently applied regimens for the treatment of patients with cancers of the gastrointestinal tract, breast, and head and neck. Unfortunately, a large variation in the clearance of 5-FU has been observed between patients, suggesting that some patients might receive nonoptimal 5-FU doses. However, therapeutic drug monitoring of 5-FU has been shown to result in reduced intra- and inter-individual variability in 5-FU plasma levels and pharmacokinetically guided dose adjustments of 5-FU-containing therapy results in a significantly improved efficacy and tolerability. To date, compartmental Michaelis-Menten elimination-based modeling has proven to be a sensitive and accurate tool for analyzing the pharmacokinetics of 5-FU and to identify patients with a dihydropyrimidine dehydrogenase deficiency. These Michaelis-Menten models also allow the use of a limited sampling strategy and offer the opportunity to predict a priori the 5-FU plasma concentrations in patients receiving adapted doses of 5-FU.

Let's get personal: predicting thiopurine and fluoropyrimidine toxicity

The US FDA now recognizes the need to individualize treatment paradigms using biomarkers that predict response to therapy. In clinical practice the best example of this is TPMT testing, which is used to rationalize the starting dose of azathioprine and mercaptopurine. The more recent addition of drug metabolite monitoring means that thiopurine therapy can now be personalized to unprecedented levels. Of interest, parallels exist between TPMT deficiency as an explanation for thiopurine toxicity and DPD deficiency in fluoropyrimidine toxicity. For these drugs, variations in a single locus predict severe toxicity. However, while TPMT testing has translated into routine clinical practice, DPD testing has not. This article summarizes the recent research investigating interindividual differences in the metabolism of thiopurine and fluoropyrimidine drugs, and explores the attitudes which influence the uptake of pharmacogenetic testing.