Splenic function and infection in sickle cell anemia

The acute chest syndrome

Recent large clinical studies of the acute chest syndrome (ACS) have improved our understanding of its pathophysiology and epidemiology. However, there is still a need for better methods of distinguishing vaso-occlusion from fibrin or fat embolism, for rapid diagnostic tests to make positive identifications of microbial infection, for adjunctive therapies that would affect prognosis, and for identification of factors that influence prognosis. The difference in clinical course and severity between children and adults supports the results of current studies indicating multiple causes for ACS. The mainstay of successful treatment remains high-quality supportive care. The judicious use of transfusion therapy has a major role in preventing mortality in the absence of a specific therapy that consistently improves the clinical course.

Salmonella as a causative organism of various infections in patients with sickle cell disease

BACKGROUND

Patients with sickle cell disease (SCD) are susceptible to a variety of bacterial infections, including infections caused by Salmonella species. We sought to identify the most common infections caused by Salmonella spp. in SCD patients at our hospital, and to determine their mortality rates and susceptibility to commonly used antimicrobial agents.

PATIENTS AND METHODS

We conducted a retrospective review of all Salmonella infections in SCD patients admitted to Qatif Central Hospital during the last 11 years.

RESULTS

During the 11 years of the study, 331 episodes of Salmonella infection occurred in 319 patients. The incidence of Salmonella infection in SCD patients was 11.5% compared to only 0.65% in the general hospital population. The commonest sites of Salmonella infection were blood (42% of isolates), followed by gastrointestinal tract (23.5%) and the skeletal system (22.5%). Salmonella infection was commonly seen in patients less than 15 years of age. The case fatality rate in patients with Salmonella sepsis was 2.2% (3/139), but there were no deaths associated with other types of Salmonella infections. Ampicillin and cotrimoxazole resistance occurred in 29% and 24% of the isolates, respectively, but only 0.6% were resistant to ceftriaxone and 1.8% had intermediate resistance to ciprofloxacin.

CONCLUSIONS

Salmonella is a common cause of sepsis and osteomyelitis in patients with SCD in our locality. Empirical antimicrobial therapy should cover the likely pathogens, including Salmonella species.

Osteomyelitis and septic arthritis in sickle cell disease in the eastern province of Saudi Arabia

Patients with sickle cell disease are more susceptible to osteomyelitis and septic arthritis than the population at large. Seventy eight patients with these conditions were admitted to our hospital from April 1988 to March 1991. Thirty had sickle cell disease, 14 had the sickle cell trait and 34 had normal electrophoresis. The tibia, followed by the femur and humerus were the bones most commonly affected, and the knee was the joint most often involved. Salmonella was the commonest organism in osteomyelitis and septic arthritis in sickle cell disease, whereas staphylococcus was commonest in normal patients and those with the sickle cell trait. Antibiotics that cover these two organisms must be considered in patients with sickle cell disease who are suspected of having osteomyelitis or septic arthritis.

Splenic size and function in adult coeliac disease

Splenic scintigraphy was performed after measurement of 99Tcm-labelled heat-damaged red cell clearance in 29 patients with treated coeliac disease. Good correlation was found between splenic size and function using these techniques. 99Tcm-labelled sulphur colloid scintiscans were also performed in 24 coeliacs. Splenic volumes computed from colloid scans correlated well with those computed from red cell scans. Almost 50% of adult patients with treated coeliac disease have impaired splenic function, the incidence rising with increasing age of starting treatment. Sulphur colloid scintigraphgy provides a simple quantitative method of assessing splenic function in treated coeliac disease which can be used in exploring the possibilities of avoidance of the adverse effects of hyposplenism.

Activity of the alternative complement pathway after splenectomy: comparison to activity in sickle cell disease and hypogammaglobulinemia

Patients with sickle cell disease and individuals who have undergone splenectomy share defects of certain host defense mechanisms and a predisposition to severe pyogenic bacterial infections. Since patients with sickle cell disease can have deficient activity of the alternative complement pathway, we have tested such activity in sera from splenectomized children and adults. A new kinetic hemolytic assay has been used, and we have compared results to those obtained with sera from patients with sickle cell disease or hypogammaglobulinemia. Sera from six of 58 splenectomized individuals (10%) had defective function of the alternative pathway, compared to 10 of 62 sera from patients with sickle cell disease (16%) and 10 of 18 sera from hypogammaglobulinemic patients (56%). Deficiency of antibody, a rate-influencing component of alternative pathway activity in this system, appears responsible for deficient activity in the hypogammaglobulinemic sera. The molecular basis for the deficiency found in sickle cell disease or after splenectomy is not clear. Defective function of the alternative complement pathway could contribute to the increased predisposition to bacterial infection that exists in these three patient groups.

Polyvalent pneumococcal-polysaccharide immunization of patients with sickle-cell anemia and patients with splenectomy

To reduce the risk of infection from Streptococcus pneumoniae in hyposplenic patients we administered octavalent pneumococcal vaccine to 77 patients with sickle-cell disease and 19 asplenic persons and compared their response with 82 controls (38 age-matched normal persons and 44 normal black African children). Fifty micrograms each of pneumococcal-polysaccharide Types 1, 3, 6, 7, 14, 18, 19, and 23 were administered subcutaneously. Post-immunization serums (three to four weeks) were available from 52 of 77 patients with sickle-cell disease; the percent responding and the magnitude of the indirect hemagglutination response were comparable to those of the controls. Within two years after immunization we observed eight Str. pneumoniae infections in 106 age-matched unimmunized patients with sickle-cell disease, but none in the 77 immunized (P less than 0.025). We conclude that pneumococcal polysaccharides are immunogenic in hyposplenic patients and may protect against systemic Str. pneumoniae infection.

Overwhelming postsplenectomy infection

One of the more intriguing aspects of the spleen is the protection against certain bacterial infections afforded by its unique vascular and immune function. There have been extensive clinical surveys which indicate an incidence of overwhelming postsplenectomy infection (OPSI) above that of the disease for which the splenectomy was done. In the absence of the spleen, either congenital or subsequent to surgical removal, this overwhelming sepsis has a 50% case fatality rate. The most common infective organism has been Diplococcus (tstreptococcus) pneumoniae (D. pneumoniae). Intensive investigations indicated loss of phagocytic function of the spleen, depression of serum IgM levels, a possible suppression of the lymphocyte responsiveness, and changes in opsonin-alternative complement system as potential causes of OPSI. Preventive measures against OPSI include trials of prophylactic Phenoxymethyl Penicillin (penicillin) and pneumococcal vaccine.