Biomedical subjects

Mark C Smith

Publications and source records attributed to Mark C Smith.

4 recordsLinked to original sources

PubMed2006

Radiotoxicity after conformal radiation therapy for benign intracranial tumors.

Acoustic schwannomas, skull base meningiomas, and pituitary adenomas are benign intracranial tumors frequently managed with radiotherapy. Control rates after treatment for each of these tumors are generally high, and toxicity from treatment is relatively low. Side effect profiles depend on the tumor location, the volume treated, the dose delivered, and the presence of nearby critical structures. In addition, patient-specific factors, such as hypertension and diabetes, may increase a patient's risk for complications. This article reviews radiotoxicity after conformal radiation therapy for acoustic schwannomas, skull base meningiomas, and pituitary adenomas.

Brain Neoplasms↗

PubMed2005

Prognosis of airway obstruction and feeding difficulty in the Robin sequence.

OBJECTIVE: To evaluate the course and prognosis of airway obstruction and feeding difficulty in the Pierre Robin sequence (PRS). METHODS: Retrospective review of 60 patients with PRS between 1993 and 2002 at the University of California, Davis Medical Center. Patients were placed into diagnostic subgroups: (1) Isolated PRS; (2) Syndromic PRS (known syndrome with PRS); (3) Unique PRS (unique anomalies with PRS). Data regarding severity, duration, and management of airway obstruction and feeding difficulty were collected. RESULTS: Airway obstruction requiring intervention beyond positional therapy was seen in 28% isolated, 42% syndromic, and 58% unique PRS. One-third of patients who failed positional therapy were temporarily stabilized with a nasopharyngeal airway or endotracheal intubation. The remaining two-thirds of patients, who failed positional therapy required a surgical airway procedure. Four patients underwent mandibular distraction osteogenesis, resulting in successful decannulation or avoidance of tracheostomy. Thirteen patients underwent tracheostomy; mean duration of tracheostomy-dependence was 17.0 months in Isolated PRS and 31.7 months in Unique PRS (p < 0.01). Successful decannulation by age of 3 years was confirmed in 85% of patients who underwent tracheostomy. Tube feeding was required in 53% Isolated, 67% Syndromic, and 83% Unique PRS. Forty-two percent of PRS patients with a successful positional airway still demonstrated feeding difficulty. Short-term (0-3 months) and intermediate (4-18 months) tube feeding was more commonly required in Isolated and Syndromic PRS, while long-term (beyond 18 months) gastrostomy tube feeding was more commonly required in Unique PRS (p < 0.01). By 3 years of age, a successful oral diet was seen in 91% Isolated, 92% Syndromic, and 78% Unique PRS. CONCLUSIONS: Diagnostic subgroups based on the presence of additional anomalies help families and physicians in understanding the severity and duration of feeding and airway difficulty in PRS. Two-thirds of PRS patients who fail positional therapy may ultimately require a surgical airway procedure. Feeding difficulty can be present in the absence of clinically significant airway obstruction. Families and physicians should be encouraged that by 3 years of age, most patients were successfully taking an oral diet without airway obstruction.

Airway Obstruction↗

PubMed2004

A timing-specific memory distortion effect in young children.

It has been suggested that there are systematic distortions in children's memory for temporal durations, such that children's memory is not just less accurate than that of adults but qualitatively different. Experiment 1 replicated the memory distortion effect by demonstrating developmental change in the tendency to confuse a reference duration with one that is shorter rather than longer than it. When the long-term memory demands of the task were reduced by providing reminders of the reference duration on every trial, there were no such qualitative changes in error patterns (Experiment 2). Further evidence for developmental changes in memory distortion was found in the temporal generalization task of Experiment 3, in which stimuli were spaced logarithmically rather than linearly. In Experiment 4, a similar distortion pattern was absent in a task in which children made judgments about the pitch rather than the duration of stimuli, suggesting the effect may be specific to time estimation.

Child, Preschool↗

PubMed2004

Difluoromethylornithine-induced reversible hearing loss across a wide frequency range.

OBJECTIVES: Alpha-difluoromethylornithine (DFMO) is an antineoplastic agent that causes reversible hearing loss (HL) by an unknown mechanism. Previous neonatal gerbil studies have identified a dosing regimen of 1 g/kg per day of DFMO given for 3 weeks that results in reversible HL on click-evoked auditory brainstem response (ABR). The objectives of this study are 1) to measure HL and recovery at several frequencies in neonatal gerbils after DFMO therapy at two different dosing regimens and 2) to identify any effects of DFMO on cochlear histology. STUDY DESIGN: Prospective, nonrandomized, experimental design with placebo controls. METHODS: ABR to tone pips at 2, 4, 8, 16, and 32 kHz were recorded on 62 21-day-old Mongolian gerbils after daily subcutaneous injections of DFMO (group A at 1 g/kg, group B at 750 mg/kg) or saline from day 3 to day 20 after birth. Thirty-seven animals were retested after a 3-week drug-free recovery period. Twenty-seven animals were killed for analysis of cochlear histology. RESULTS: Animals that were administered DFMO demonstrated higher ABR thresholds across all five frequencies, with mean threshold differences of 21 to 29 dB in group A and 11 to 17 dB in group B as compared with controls. Higher thresholds were demonstrated at higher frequencies. Fewer side effects were noted at the lower dose. After a 3-week drug-free recovery period, auditory thresholds returned to pretreatment levels. No significant cochlear structural abnormalities were identified under light microscopy. CONCLUSION: An 18-day regimen of 750 mg/kg per day of DFMO given subcutaneously in neonatal gerbils causes minimal side effects with broad-frequency HL that, after 3 weeks of recovery, is fully reversible.

Analysis of Variance↗