Hb S (HBB: c.20A>T) Characteristics by High Performance Liquid Chromatography in Patients with Sickle Cell Disease Receiving the Novel Agent Voxelotor.

Voxelotor is a novel agent in the management of sickle cell disease. It is an inhibitor of Hb S (HBB: c.20A>T) polymerization that reversibly binds to hemoglobin (Hb), stabilizing it in the oxygenated state that has been shown to reduce hemolysis and to improve anemia. Four patients in our institution are receiving treatment with Voxelotor as part of clinical studies. All four showed a characteristic change in the appearance of Hb S by high performance liquid chromatography (HPLC) soon after commencing treatment. A second peak was identified eluting at the Hb D window. Cellulose acetate membrane and agar gel electrophoresis only identified a band at the Hb S position. The patients' Hb level or clinical conditions were not adversely affected. Our findings indicate that patients receiving Voxelotor invariably display this unique pattern by HPLC. As there will be an increasing number of patients treated with this agent, it is important to be aware of this characteristic HPLC appearance for diagnostic and treatment monitoring purposes.

Automated Red Cell Exchange in the Management of Sickle Cell Disease.

Red cell transfusion represents one of the cornerstones of the chronic management of sickle cell disease, as well as its acute complications. Automated red cell exchange can rapidly lower the number of circulating sickle erythrocytes, without causing iron overload. Here, we describe our experience, having offered this intervention since 2011. A transient reduction in the platelet count by 61% was observed after the procedure. This was not associated with any haemorrhagic complications. Despite exposure to large volumes of blood, the alloimmunisation rate was only 0.027/100 units of red cells. The absence of any iron loading was confirmed by serial Ferriscans, performed over a number of years. However, patients with advanced chronic kidney disease showed evidence of iron loading due to reduced innate haemopoiesis and were subsequently switched to simple transfusions. A total of 59% of patients were on regular automated red cell exchange with a history of recurrent painful crises. A total of 77% responded clinically, as evidenced by at least a 25% reduction in their emergency hospital attendance for pain management. The clinical response was gradual and increased the longer patients stayed on the program. The earliest sign of clinical response was a reduction in the length of stay when these patients were hospitalised, indicating that a reduction in the severity of crises precedes the reduction in their frequency. Automated red cell exchange also appeared to be beneficial for patients with recurrent leg ulcers and severe, drug resistant stuttering priapism, while patients with pulmonary hypertension showed a dramatic improvement in their symptoms as well as echocardiographic parameters.

Fat Embolism Syndrome in Sickle Cell Disease.

Fat embolism syndrome is a devastating complication of sickle cell disease resulting from extensive bone marrow necrosis and associated with high mortality rates, while survivors often suffer severe neurological sequelae. Despite that, the syndrome remains under-recognised and under-diagnosed. Paradoxically, it affects exclusively patients with mild forms of sickle cell disease, predominantly HbSC and HbSß+. A significant number of cases occur in the context of human parvovirus B19 infection. We provide here a brief summary of the existing literature and describe our experience treating 8 patients in our institution. One patient had HbSS, 6 HbSC and 1 HbSß+. All patients developed type I respiratory failure and neurological involvement either at presentation or within the first 72 h. The most striking laboratory abnormality was a 100-fold increase of the serum ferritin from baseline. Seven patients received emergency red cell exchange and 1 simple transfusion. Two patients (25%) died, 2 patients (25%) suffered severe neurological impairment and 1 (12%) mild neurological impairment on discharge, while 3 (38%) patients made a complete recovery. With long-term follow-up, 1 patient with severe neurological impairment and one patient with mild neurological impairment made dramatic improvements, making the long-term complete recovery or near complete recovery rate 63%. Immediate red cell exchange transfusion can be lifesaving and should be instituted as soon as the syndrome is suspected. However, as the outcomes remain unsatisfactory despite the increasing use of red cell exchange, we suggest additional therapeutic measures such as therapeutic plasma exchange and pre-emptive transfusion for high risk patients.