Difficulties in Immunohaematology : The Weak D Antigen

Background

The Rh blood system is one of the most polymorphic and immunogenic systems known to humans. The expression of Rh blood group antigen is complex. The Rh D antigen is the most important of the antigens that constitute the Rh antigen system. In most cases, D antigen can easily be detected. However, due to variability of expression, weak forms antigen are encountered. The reactivity of weak D with antisera is variable and presents as a problem in blood banking.

Methods

A retrospective analysis for a five-year period was done. Blood samples that were negative for Rh D by immediate spin tube method were tested for weak D antigen by additional lab tests.

Result

Of 34932 serial Rh grouping tests done in our Blood Bank, the incidence of weak D Rh antigen was 0.189%. All these were confirmed by the antiglobulin test.

Conclusion

These patients present as a problem for the blood banker and a curiosity to the clinician. Although uncommon, all health care workers should be aware of this entity to avoid anti D alloimmunisation.Key Words: Weak D, Rh Blood Group     

A prospective analysis of intraoperative electromyographic monitoring of posterior cervical screw fixation

OBJECTIVE: This is a prospective study of 26 patients undergoing posterior cervical spine instrumentation with lateral mass or pedicle screws to determine the correlation between intraoperative screw stimulation thresholds and the position of posterior cervical lateral mass and pedicle screws. METHODS: One hundred forty-seven posterior cervical screws (122 lateral mass screws and 25 C7 pedicle screws) in 26 patients were electrically stimulated intraoperatively and stimulation thresholds recorded. Computed tomography (CT) scans were taken postoperatively and were evaluated independently to assess screw position. Electromyographic (EMG) thresholds and CT data were compared to assess the accuracy of the EMG screw stimulation technique in detecting screw malposition. RESULTS: Intraoperative electrical stimulation was accurate in verifying screw position. A stimulation threshold of 15 mA provided a 99% positive predictive value (89% sensitivity, 87% specificity) that the screw was within the lateral mass or pedicle. Stimulation values of 10-15 mA provided a 13% predictive value (66% sensitivity, 90% specificity) that the screw was within the lateral mass or pedicle. A stimulation value of <10 mA provided a 100% predictive value that the screw was malpositioned (70% sensitivity, 100% specificity). CONCLUSIONS: Intraoperative evoked EMG monitoring is a valuable tool in posterior cervical instrumentation using lateral mass and pedicle screws. Stimulation thresholds in this study correlated with screw position. Stimulation values of >15 mA reliably predict acceptable screw position. Values between 10 and 15 mA are generally associated with acceptable screw position, although exploration is recommended. Values below 10 mA are associated with screw malposition and warrant exploration, repositioning, and possible removal.     

Infection in the neuroischemic foot

Infection in the neuroischemic foot can lead to cellulitis, which often progresses to necrosis as a result of septic vasculitis. Therefore, it is important to diagnose infection early. However, the signs and symptoms of infection are diminished in the neuroischemic foot. Microbiological investigation is essential. Severe infection needs intravenous antibiotic therapy and urgent assessment of the need for surgical drainage and debridement. Infected neuroischemic feet need vascular assessment and intervention where appropriate. It is important to maintain strict metabolic control and optimize cardiovascular function. Recent modern approaches based on multi-disciplinary clinics have resulted in improved results in the management of infection in the ischemic diabetic foot.     

Pseudoclaudication as a manifestation of diabetic neuropathy.

We present the case of a 64-year-old male Type 1 diabetic patient with painful diabetic neuropathy masquerading as intermittent claudication. Examination of the peripheral circulation (both arterial and venous) was normal. An MRI scan excluded lumbar spinal stenosis and nerve root compression as the cause of claudication. The case suggests that, in the absence of other identifiable causes and in the presence of peripheral diabetic neuropathy, "intermittent claudication" may be due to the neuropathy itself.     

Age- and sex-related variation in song-control regions in Cassin's finches, Carpodacus cassinii

Male Cassin's finches (Carpodacus cassinii) sing long, complex songs that incorporate many elements mimicked from other species. Although one-year-old males (males in their first breeding season) are sexually competent and do breed, they sing a simpler song (fewer syllable types) than do males two or more years old (called after-second-year males). Females do occasionally sing, but with much less stereotypy and complexity than breeding males of any age. We collected brains from free-living breeding after-second-year males (identified by their red plumage), one-year-old males (identified by their female-like brown plumage), and adult females to examine sex- and age-related differences in three song-control nuclei: HVC, Area X and RA. Nuclei volumes were reconstructed by measuring the Nissl-defined area in every second section. There was a large sex difference in all three nuclei, with female volumes 40-50% that of males. There was no difference in HVC volume between age classes of males. However, one-year-old (brown) males had significantly larger Area X volume than did the older (red) males, with red males' Area X about 75% the volume of brown males'. These data raise questions regarding the functional significance of Area X and related nuclei in relation to song development in vocal mimics.