Sickle Cell Disease (Lancet 2017, BCSH, GTG 2011)

12,500 SCD in UK (9% on LT transfusion programme)

 

Intro

Caused by inheritance of the sickle mutation on the HBB gene (Glu6Val, bs)

Sickle Cell Trait = HbAS

Sickle Cell Anaemia = HbSS

Possible sickling compound heterozygotes = HbSC, HbS/b0, HbS/b+, HbSC, HbSOArab,

 

In West Africa, SCD responsible for 16% of all deaths in <5 year olds

In Jamaica, 10% of SCD infants die between 6-12 months of age

In the UK, 99% survival to age of 16 years

 

Pathophysiology

In hypoxic states, erythrocytes become rapidly, but reversibly, deformed.

Intracellular polymerization of the abnormal HbS molecule stretches cell into rigid sickle form

Sickled cells cause vaso-occlusion, along with many other cellular and plasma factor interactions

--> Cycle of repeated ischaemia and inflammation

Re-oxygenation restores the normal red cell shape. Cells cycle in and out of this state until forced into intravascular haemolysis or extravascular removal by the reticendothelial system.

 

HbS is a low oxygen affinity haemoglobin --> right shift on the oxygen dissociation curve --> partly explains the chronic anaemia in SCD (which is not all due to haemolysis)

 

Annual Review Clinic

 

Height, weight, BP, O2 Sats

 

No. & severity of crises in the last year

Analgesic use

Cardiovascular symptoms

Iron overload

Other – AVN, ulcers, osteomyelitis, disc protusions

Education, Employment and Training

Family Planning

Medication compliance – folic acid, pencillin, HU, ACEI, chelators

 

Bloods – FBC, U&E, LFT, Ferritin, Hep B Ab titre, Vit D

Red cell Genotyping

Echo

 

Ophthalmology review

Vaccinations – 5 yearly pneumococcus, seasonal ‘flu, Hep B

A&E Management plan

NHR Register

 

Transfusion (See section in Transfusion tab for more)

 

Extended phenotype at baseline

-       Rh, Kell, Jk, Fy & Ss

-       Check U if S-, s-

-       Offer genotyping

 

Blood Product Requirements

-       Rh and Kell matched. R0 for R0 where available (rr alternative)

-       Hb S negative

-       RBC <10 days old for top-up, <7 days for Exchange

 

TAPS Trial (Transfusion Alternatives Preoperatively in Sickle Cell Disease)

-       Pre-Op transfusion if Hb <90 reduces risk of acute chest crisis post-op

-       Trial stopped early due to clear benefit in favour of pre-op transfusion.

 

Top-Up Transfusion

-       Preferred for treatment of acute severe anaemia

-       E.g. aplastic crisis, acute splenic or hepatic sequestration, >20g/l drop during a painful crisis

 

Exchange Transfusion

-       Preferred for immediate or sustained reduction in complications of SCD

-       Bonus: Achieves neutral or negative iron balance

-       Manual exchange: Aim to exchange 30% of blood volume – 4 units out, 3 + saline in.

-       Definite indications

o   Acute Stroke

o   Multi-Organ Failure, Mesenteric-Girdle Syndrome, Sepsis, Cholestasis

o   All SCD for high-risk surgery

 

Hydroxycarbamide (BSH 2018)

 

Mechanism of Action:

HU is a ribonucleotide reductase inhibitor --> depletes intracellular deoxynucleotide pools required for DNA synthesis and repair --> cytostatic effect.

This alteration to the cell cycle kinetics, along with effects on guanylyl cyclase and SAR1, increases HbF production.

HbF inhibits intracellular HbS polymerization, and higher HbF% associated with reduced morbidity and mortality.

 

Benefits

Reduces mortality

   -  17 years of observational follow-up from the Multicentre Study of Hydroxyurea (MSH) found hydroxycarbamide use was associated with a 40% reduction in adult mortality.

Reduces Acute Pain and Chest Crises

   -   MSH 1995 - double-blind, placebo controlled trial of hydroxycarbamide --> 40% reduction in median number of painful crises over two years (4.5 vs 2.5), median time to first crisis doubled and incidence of ACS reduced.

Reduces hospitalisations and pain in the community

   -   Shown in repeated observational studies

Prevents first stroke?

   -   HU has not been formally assessed as first line therapy for children with raised transcranial Doppler velocities (TCD).

   -   A switch to HU after a minimum of one year of initial transfusion has been shown to be non-inferior to ongoing transfusion, provided that there is no MRI evidence of vasculopathy (TWiTCH 2016)

Prevents organ damage

   -   Evidence is not entirely clear or in agreement but there may be beneficial effects of HU on preserving splenic function, improving renal dysfunction, improving oxygen saturation, preventing priaprism and improving pain in avascular necrosis.

   -   There is no evidence at present to suggest HU is beneficial in preventing pulmonary hypertension.

 

Which HbSS and HbS/BetaO patients should be on HU?

 

Offer to:

Infants aged 9-42 months regardless of clinical severity to reduce sickle complications

Children aged >42 months, teenagers and adults to reduce mortality

Children on a regular transfusion schedule for primary prevention of stroke, after 1 year of transfusion and provided there is no MRI evidence of vasculopathy

 

Recommend to adults and children who have:

3+ mod-severe pain crises in a 12 month period

Sickle pain that interferes with daily activities

A history of severe and/or recurrent ACS

Chronic anaemia that interferes with daily activities

Chronic hypoxia

 

Also give consideration to potential benefits listed above regarding prevention of organ damage and discuss these issues with patients.

 

Concerns about HU

 

Short term Side Effects

   - Transient, reversible myelosuppression

   - Mild GI symptoms

   - Skin and nail hyperpigmentation, hair thinning

   - Skin ulcers are reported but are not any more frequent that in those not on HU

Leukaemogenesis

   - There is no risk of leukaemogenesis when HU is used for the treatment of haemoglobinopathies

Growth and Development

   - There is no evidence to show growth or development is impaired by HU

Fertility

   - There is no evidence that HU affects fertility.

   - However, there is some suggestion of an effect of HU on male spermatogenesis in laboratory studies. It is recommended that post-pubertal male patients who are due to start HU for the first time should be offered sperm cryopreservation.

Teratogenicity

   - There is laboratory evidence of teratogenicity at suprapharmacological doses.

   - Patients on HU should use contraception

   - Women who become pregnant whilst taking HU require careful review of the risks of stopping HU (i.e. increased risk of sickle-related pregnancy complications) as this may outweigh the possible risk of teratogenicity.

 

Dosing

 

Adults: Start at 15mg/kg/day (rounded up to nearest 500mg)

Children: Start at 20mg/kg/day (rounded up to nearest 500mg)

 

Increase dose by 5mg/kg/day every 8-12 weeks aiming for a neutrophil count of 2-3.

Stop if the neutrophil count falls below 1.

This is the maximum tolerated dose.

 

Aim to deliver the maximum tolerated dose as evidence to suggest best outcomes with this approach.

 

Adjust dose for renal impairment.

 

Continue for minimum of six months before assessing response to therapy.

Failure to respond should be assessed by a lack of clinical response and not by laboratory values.

 

Treatment should be continued during hospital admissions, unless for febrile neutropenia.

 

New Drugs

 

Rivipansel

-       P Selectin inhibitor --> inhibits the adhesion/activation of leukocytes

 

Crinzalizumab

-       Anti-P Selectin Antibody

-       Administered whilst well in combination with HU

-       SUSTAIN Trial – Phase 2. 45% fewer crises vs Control. SAE in 55/151, 5 deaths

 

Others

-      Canakinumab, Voxelotor, L-Glutamine, Butyrate, Gardos channel blockers, lenalidomide, azactidine

 

Pregnancy Plan

 

Pre-Conception

Discuss risks to mother– perinatal mortality, acute crises

Discuss risks to fetus - fetal growth restriction, premature labour

Screen father for Hbpathy – if HbS, B-thal, O-Arab, HbC, D-Punjab offer prenatal diagnosis

Review systems – Pul HTN, Iron Overload, Retinopathy, HTN, Renal function

Optimise meds – Pen V, Folic Acid, Vaccinations

Stop HU three months prior to conception

Stop ACEI before conception

 

Antenatal

Consultation

MDT, Fetal Medicine Unit

Screen for end organ damage if not done pre-conception

Avoid dehydration, extreme temperatures & overexertion

 

Scans

Offer viability scan at 7-9 weeks

Routine 1st trimester scan at 11-14 weeks

Routine anomaly scan at 20 weeks

Additional monthly growth scans from 24 weeks

 

Other

BP &  Urinalysis at every visit

Urine culture monthly

 

Treatment

Aspirin from 12 weeks (reduces risk of pre-eclampsia)

Prophylactic LMWH during hospital admissions

?Prophylactic RBC transfusion - no clear evidence, patient-by-patient basis

 

Intrapartum

Offer Induction of labour after 38+0 weeks (any mode of delivery)

If known red cell antibodies, crossmatch blood for delivery in advance

Intrapartum fetal heart rate monitoring is recommended (increased risk of fetal distress)

 

Postpartum

Prevent dehydration, maintain O2 sats.

LMWH prophylaxis 7 days post NVD, 6 weeks post C-Section

Test neonate for sickle

 

 

Iron Chelation

 

1 unit RBC contains 200-250mg Iron

Aim to start chelation after first 10-20 units RBC transfusion, when ferritin >1000ng/ml or when MRI liver demonstrates >7mg/gram of dry weight (LIC) iron loading

Consider stopping when ferritin <500 or LIC <5mg/gram of dry weight

 

Approx 450 SCD patients in UK on iron chelation

 

Assessing iron load:

-       Ferritin

-       T2* Cardiac MRI

-       FerriscanTM MRI or biopsy for liver

 

Aims

1.     Prevent harmful effects of free iron

2.     Prevent or reverse organ damage

3.     Maximise quality of life

4.     Prolong survival

 

Desferrioxamine (Desferol) DFO

-       SC/IV continuous infusion, aiming for 8-12 hours daily (24 hours if tolerated)

-       20-60mg/kg/day

-       Risk of side effects reduced by a ratio of mean daily dose(mg/kg) / ferritin kept <0.025

-       Side Effects

o   Hearing & Visual loss (3 monthly screening of both)

o   Yersinia GI infection (mimics appendicitis)

o   Arthralgia / Myalgia

 

Deferiprone (Ferriprox) DFP

-       Oral tablet TDS

-       75-100mg/kg/day

-       Licensed as monotherapy if desferol contraindicated or ineffective

-       Superior cardiac clearance compared to desferol

-       Side Effects

o   GI disturbance

o   Small joint arthritis

o   Agranulocytosis

 

Deferasirox (Exjade, Jadenu) DFX

-       Exjade - Oral dispersible tablet, OD, 10-40mg/kg/day

-       Jadenu – Coated tablet, 1/3 the dose of Exjade, usually better tolerated (fewer GI SE)

-       10-40mg/kg/day

-       Better tolerated but slower iron clearance

-       Side effects:

o   GI ulcers

o   Rash

o   Renal impairment

o   Transaminitis

 

Stroke Prevention in Children

 

 

Before introduction of TCD, 5-15% of children suffered acute stroke

 

STOP 1998 – 1o prevention - TCD >200cm/s --> regular transfusion prevents stroke (92% RR)

STOP2 2005 – 1o prevention - ?Can you stop transfusing --> No, the stop arm had new strokes

SWiTCH – 2o prevention - ?Can you switch from transfusion to HU after 30 months --> No.

TWiTCH 2016 – 1o prevention - ?Transfusion + HU & eventually stop transfusion --> Yes

 

Transplant

 

Only curative procedure

Very difficult to choose right patient at the right time

Best outcomes if proceed prior to organ damage, but want to select only severely affected patients due to the morbidity and mortality associated with HSCT (including infertility).

Most success so far in matched sibling, bone marrow harvest, myeloablative HSCT in children.

Effective in preventing future clinical complications of SCD.

In adults, 87% EFS reported with matching sibling RIC allografts.

Unrelated transplant currently appears unsafe for widespread use. Higher mortality and GVHD.

 

Gene Therapy Autografts?

 

-       Stem cell collection --> Ex vivo gene therapy to add HbA gene --> myeloablative conditioning and re-infusion of modified autologous stem cells