Abstract:
Atypical hemolytic uremic syndrome (aHUS) is an infrequently encountered
complement-mediated thrombotic microangiopathy (TMA) usually associated
with germline variants in genes of the complement system. Clinical
findings of microangiopathic hemolytic anemia, thrombocytopenia, and
acute kidney injury (AKI) with severe hypertension arise due to aberrant
complement protein activation in the circulation and significant
endothelial damage. Transplant-associated thrombotic microangiopathy has
been increasingly recognized after high dose carboplatin, etoposide, and
melphalan-chemotherapy followed by autologous hematopoietic stem cell
rescue for treatment of children with neuroblastoma (NB). We report the
case of a 13-month-old boy with metastatic neuroblastoma who developed
aHUS during the first cycle of induction chemotherapy. Germline testing
revealed a Complement factor H (CFH) gene mutation, Cys357Arg,
which is currently classified as a variant of uncertain significance
(VUS), although likely pathogenic based on molecular modeling as well as
this patient’s clinical presentation. The patient has been successfully
managed with complement blockade therapy with no recurrence of disease.
We review presentations of neuroblastoma with hypertension, along with
AKI and thrombocytopenia, to raise awareness about the potential for
aHUS in patients with newly diagnosed NB.
Introduction:
Neuroblastoma (NB) is classically a catecholamine-secreting tumor that
arises from primitive ganglionic cells along the sympathetic chain or
adrenal medulla1. Some NB tumors spontaneously
regress, while others are highly aggressive and progressive despite
intensive chemotherapy1. The initial presentation of
NB can include severe uncontrolled hypertension due to tumor compression
of the renal vasculature and parenchyma and/or from excess catecholamine
release1. When hypertension is associated with
hemolytic anemia, thrombocytopenia, and acute kidney injury (AKI), it
should raise immediate concern for atypical hemolytic uremic syndrome, a
type of thrombotic microangiopathy (TMA) seen in those with a genetic
predisposition often triggered by infection, malignancy or chemotherapy
leading to abnormal activation of the complement cascade leading to
endothelial and end organ damage2. Atypical HUS (aHUS)
is a potential complication of autologous hematopoietic stem cell
transplantation (HSCT) after treatment with high dose carboplatin,
etoposide, and melphalan (CEM) for neuroblastoma, particularly in those
with genetic variants in complement genes2,3. However,
it has not previously been reported following initiation of induction
chemotherapy for a patient with high-risk NB.
Case Presentation:
A 13-month-old boy born full term presented to the emergency department
(ED) with an enlarging left scalp mass and clinical concern from the
pediatrician that the differential diagnosis included non-accidental
trauma. On evaluation in the ED, vital signs were temperature of 38°C,
heart rate 150 beats per minute, respiratory rate 32 breaths per minute
with 100% oxygen saturation on room air, and blood pressure 105/72,
which was within normal limits for systolic blood pressure and above the
99th percentile for diastolic blood pressure. His
physical exam was pertinent for a 3 cm firm non-indurated and non-tender
swelling of the right temporo-parietal scalp, as well as bilateral
periorbital edema, ecchymoses of the upper eye lids, and bilateral
subconjunctival hemorrhages. Abdominal exam was notable for a 7 cm firm
mass in the left upper quadrant extending past the umbilicus.
Computerized tomography (CT) of the head demonstrated a 14mm lesion in
the right pterion with intracranial soft tissue extension causing mild
mass effect on the right frontal operculum, a 5 mm extracranial soft
tissue lesion, and a 4 mm right parietal lesion with intracranial
extension. CT neck, chest, abdomen, and pelvis revealed a large complex
mass arising from the right adrenal gland measuring 7.4 x 7.3 x 8 cm, as
well as several areas of increased enhancement within the liver
measuring as large as 7.4 x 9.1 cm. Iodine-123 meta-iodobenzylguanidine
(MIBG) scan demonstrated increased radiotracer uptake in the large
heterogenous right adrenal mass, left hepatic lobe, left iliac wing,
left proximal femur head, and right proximal femur and right ischial
bones as well as right temporal region and bilateral orbital bone
lesions, consistent with the diagnosis of metastatic neuroblastoma.
Bilateral bone marrow biopsy demonstrated 5% metastatic neuroblastoma
with immunohistochemical stains for synaptophysin highlighting the tumor
cells. Our patient had high-risk NB based on age, stage of disease, and
tumor molecular finding of MYCN amplification, and he was treated
as per a high-risk induction regimen4 starting with 5
days of topotecan and cyclophosphamide. On day 6, labs were notable for
a rising creatinine of 0.84 mg/dL from a baseline of 0.40 mg/dL
(age-specific normal range <0.5 mg/dL) and decreasing sodium
to 128 mEq/L from normal levels, which was thought to be mild
chemotherapy-induced AKI and hyponatremia that was managed
conservatively with fluid restriction. On day 7, he developed oliguria
and severe hypertension above the 99th percentile for
age. Isradipine and more intensive antihypertensive management had no
effect. Blood work demonstrated unexpected laboratory evidence of
hemolysis, including rising lactate dehydrogenase and indirect
hyperbilirubinemia, as well as undetectable haptoglobin. A peripheral
blood smear was notable for multiple schistocytes per high power field,
raising concern for TMA. While ADAMTS13 was pending, in the absence of
diarrhea and concurrent E. coli infection or suspected trigger
for HUS and a PLASMIC score of 3, he was trialed on plasma exchange
(PLEX), which did not improve his clinical status, decreasing the
likelihood of thrombotic thrombocytopenic purpura. A diagnosis of aHUS,
instead of other types of TMA, was supported by: CH50 and sC5b-9
elevated at >60 U/mL (normal range 31 – 60 U/mL) and 307
ng/mL (normal range <244 ng/mL), respectively. A genetic
susceptibility aHUS panel revealed a Complement factor H (CFH)gene mutation, Cys357Arg, which while classified as a variant of
uncertain significance, may be pathogenic due to its effect on protein
structure and this patient’s clinical course (Figure
1)5,6. We performed molecular modeling using the open
source software, PyMol, and found that the mutation abolishes a
predicted intramolecular disulfide bone, thus causing significant
structural change to the protein with likely impact on enzymatic
function 5,6. The patient was started on eculizumab
treatment, initially at a dose of 300 mg weekly per the recommendations
from the drug manufacturer, after receiving quadrivalent meningococcal
conjugate and meningococcal group B vaccines and starting Penicillin VK
for meningococcal prophylaxis.
Due to his degree of critical illness with declining respiratory status
attributable to intractable fluid overload, the patient was intubated
and started on continuous veno-venous hemofiltration (CVVH). CH50 began
to downtrend after the second dose of eculizumab, while his clinical
status and renal function remained tenuous until the fourth dose of
eculizumab treatment, at which point he was extubated and CVVH was
discontinued successfully (Figure 2). By day 30 in his first
chemotherapy cycle, his clinical status and correlative laboratory
markers, including peripheral schistocytes, creatinine, CH50 and
haptoglobin, demonstrated stable improvement (Figure 2) and eculizumab
dosing was spaced to every 2 weeks. After a 5-week delay in conventional
induction treatment to allow recovery, during which he received bridging
chemotherapy with irinotecan/temozolomide, he completed four additional
cycles of chemotherapy, including re-challenge of cyclophosphamide and
topotecan, which had been the suspected trigger for aHUS. He experienced
no exacerbation of his aHUS findings apart from a mild transient
increase in his creatinine after his first re-challenge with
chemotherapy approximately 30 days after his initial presentation
(Figure 2). After achieving a partial response to chemotherapy and
undergoing surgical resection of his primary tumor, he underwent tandem
autologous stem cell transplant (ASCT), first with a conditioning
regimen of thiotepa and cyclophosphamide and second with a CEM
conditioning regimen7. In recognition of the increased
risk of transplant associated TMA (TA-TMA), in particular with CEM
conditioning, eculizumab dosing was intensified to weekly during his
first ASCT and to twice weekly during his second with frequent
monitoring of CH508. During radiotherapy and five
cycles of immunotherapy with dinutuximab, GM-CSF and cis-retinoic acid,
he received weekly eculizumab and maintained stable aHUS marker labs.
Eculizumab was spaced again to biweekly maintenance therapy, and after 4
months in remission, he was changed to ravulizumab, which has been dosed
monthly. At 20 months after completion of anti-cancer therapy, he has no
evidence of tumor recurrence or reactivation of aHUS.
Discussion:
Approximately 2% of children with neuroblastoma can present with
hypertension, flushing, and periods of diaphoresis attributed to
increased catecholamine secretion 1. In one
retrospective review of 10 patients with both NB and hypertension, four
required more than three antihypertensives, including alpha/beta
blockade9. The hypertension was reported to resolve
spontaneously, reflective of decreasing tumor burden in response to
chemotherapy, or after surgical resection of the primary tumor. When
hypertension rapidly worsens or is associated with hemolysis,
thrombocytopenia, and AKI, as noted in our patient, the findings could
be attributed to aHUS, which may be more common than previously
appreciated10.
Thrombotic microangiopathy describes a variety of conditions
characterized by microangiopathic hemolytic anemia, thrombocytopenia,
and AKI. Thrombotic thrombocytopenic purpura, a TMA, is a condition in
which lack of ADAMTS13, either due to autoantibodies or congenital
mutations, results in excess amounts of high molecular weight von
Willebrand multimers. This leads to intravascular micro-thrombosis,
hemolysis and damage to the endothelial surface11.
This condition, which tends to improve following PLEX therapies, is more
often characterized by a severe drop in platelet count and mild rise in
creatinine11. Hemolytic uremic syndrome (HUS), another
TMA, is characterized by similar features and specifically associated
with Escherichia coli Shiga toxin2. Atypical
hemolytic uremic syndrome (aHUS), less commonly seen, occurs due to
dysregulation of the complement pathway, leading to intravascular
hemolysis2. Endothelial damage and end organ damage,
including significant increase in creatinine, results from uncontrolled
complement mediated lysis, stiffening of red blood cell membranes,
deposits of complement fragments, and microthrombi2.
Thrombocytopenia results from both platelet consumption and enhanced
platelet aggregation and is typically milder than that seen in
TTP12. Transplant-associated thrombotic
microangiopathy (TA-TMA), an HUS seen in approximately 39% of children
and young adults undergoing HSCT 13, is associated
with CEM-containing conditioning regimens commonly used as part of
consolidation therapy for neuroblastoma, post-transplant infection, and
genetic variants in complement regulatory genes and more recently has
been defined as a possible secondary HUS that typically resolves with
removal of a suspected trigger3,8,14. Testing for
TA-TMA tends to occur after the first ASCT and includes monitoring of
blood pressure, urinalysis, and soluble C5b9. aHUS can be diagnosed with
clinical evaluation and common blood tests, including a complete blood
count, urinalysis and comprehensive metabolic panel, and early
recognition and then treatment of this condition when it is severe can
allow significant recovery of kidney function.
Germline aberrations have been implicated in 40-60% of patients with
aHUS 15. Our patient was found to have a heterozygous
pathogenic mutation in the CFH gene. CFH is a complement
inhibitor and is present as a soluble protein that prevents complement
activation when bound to cell surfaces in the human
body16. When CFH does not function to regulate the
complement pathway, uncontrolled activation results, leading to
endothelial damage and end organ damage16. Mutations
in this gene have been associated with multiple conditions, most notable
of which is aHUS, with 15% of individuals having deletions or
duplications, most of which are inherited in an autosomal dominant
pattern17,18. Germline variants in other complement
associated genes, such as CFH , MCP (CD4), CFI, C2, CFB,
CFHR1, CFHR3, CFHR4, CFHR5, diacylglycerol kinase epsilon (DGKE)and thrombomodulin (THBD), have also been implicated in 50% to
60% of all aHUS cases 17,19. Based on an
analysis of 2317 patients demonstrating at least one deleterious
mutation in a complement-associated gene 54% of the time, germline
genetic testing for aHUS is recommended for patients with persistent
thrombocytopenia or reported ADAMTS13 levels
<50%19. However, a congenital
predisposition is not typically sufficient for clinical manifestations
of aHUS; most patients who become symptomatic experience a trigger,
which can include infection, systemic lupus erythematosus, or
chemotherapy19, the latter of which our patient was
exposed to in the setting of a catecholamine-secreting malignancy.
TA-TMA in patients with high-risk neuroblastoma is not well
characterized with incidence ranging from 7% to 30% of patients,
particularly in those receiving CEM-containing regimens in preparation
for autologous HSCT20,21. Our patient developed aHUS
following his initial chemotherapeutic regimen, containing
cyclophosphamide, prior to any CEM-containing regimen or known trigger
for secondary HUS, raising concern for an underlying genetic
predisposition to aHUS. While there was a risk of recurrence with
re-exposure to cyclophosphamide, we chose to move forward with the
chemotherapeutic agent that would best treat his underlying malignancy
and continue complement blockade to manage his aHUS.
Eculizumab and ravulizumab are FDA-approved monoclonal antibodies that
target terminal complement C5 to try to abrogate aberrant complement
activation, which therefore leads to improvement in thrombotic
microangiopathy, thrombocytopenia, estimated glomerular filtration rate,
and event-free survival, as well as improvement in health-related
quality of life 22. Early recognition of TMA and
administration of complement blockade decreases rates of end stage renal
disease (ESRD)23. Without the addition of complement
inhibitors, as few as 25% of patients with TA-TMA achieve disease
remission 13. In fact, patients with TA-TMA have been
reported to require higher or more frequent dosing of complement
blockade to achieve an adequate clinical response8,
which is why we managed our patient conservatively with more frequent
dosing during ASCT. While initiation of complement blockade can be
effective in these patients at diagnosis, if discontinued prematurely,
aHUS may recur 17,24,25. In these cases, symptoms may
not be as responsive to re-initiation of complement blockade, leading to
increased morbidity from long term sequelae of aHUS17. For these reasons, as well as the germlineCFH mutation in our patient, complement blockade has been
continued after completion of all anti-cancer therapy. For convenience
purposes, the patient was transitioned to ravulizumab, which is
re-formulated from eculizumab to extend its terminal elimination
half-life to allow a dosing regimen of every 4-8 weeks, depending on
patient weight26. Ravulizumab was shown to be
effective in patients <18 years old with documented aHUS who
had demonstrated an appropriate clinical response to eculizumab with
stable aHUS lab values27.
This patient’s case led us to reconsider how we evaluate hypertension in
children with NB. The clinical findings and congenital predisposition to
aHUS prompted an aggressive management strategy with eculizumab that
maintained complement inhibition during intensive phases of NB
treatment. The findings of aHUS may be more common than currently
reported given that hypertension and lab abnormalities are often
attributed to tumor and/or chemotherapy effect. Delayed recognition of
aHUS can result in ESRD and death 28. There are
testing paradigms for TA-TMA that can be applied to patients with aHUS
as described in our report, though there is no consensus regarding
genetic predisposition testing for at-risk patients (e.g., prior to ASCT
for patients with high-risk NB)13,20,29-31. We
consider it reasonable to pursue germline testing for aHUS in patients
with high-risk NB, particularly when those patients develop hypertension
and/or have additional concerning laboratory abnormalities, even if ASCT
has not yet commenced. Those with germline predisposition to aHUS may
benefit from long-term complement inhibition initiated early in
treatment course, though a coordinated effort by treating physicians to
catalog and study this population of patients is needed. Understanding
individual risk factors for aHUS in each patient will allow providers to
better care for those with NB to minimize toxicity and sequelae of aHUS
from through early detection and rapid initiation of therapy.