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A 4-week-old Caucasian girl presented to her local accident and emergency department with a one-day history of difficulty breathing. She had been born at 37 weeks gestation by spontaneous vaginal delivery. The pregnancy had been complicated by mild intrauterine growth restriction (weight on the 2nd centile) and maternal genital chlamydia infection at 18 weeks gestation, which had been treated with erythromycin. The delivery was uneventful but she developed respiratory distress at 24 h of age and was admitted to the neonatal unit. The results of investigations undertaken during the early neonatal period are shown in table 1. She was treated with intravenous penicillin and gentamicin for presumed pneumonia, although no organism was isolated. She improved and was discharged from hospital aged 2 weeks. On examination in the A&E the following were noted:
Oxygen saturation of 88% in air
Right basal crepitations
No dysmorphic features
Weight and head circumference on the 2nd centile.
The admitting registrar thought the chest x ray showed right middle and lower lobe pneumonia. In view of the history of maternal genital chlamydia infection, chlamydia pneumonia formed part of the differential diagnosis. Chlamydia IgG and IgM, as well as eye swabs for Chlamydia PCR were therefore sent. As the diagnosis of Chlamydia pneumonia was less likely than typical pneumonia given the full course of treatment her mother had received during pregnancy, she was started on intravenous cefotaxime and gentamicin. Supplementary oxygen was given via a nasal cannula.
Neonatal chlamydia infection is contracted during parturition. Up to 70% of infants born to mothers with genital chlamydia infection are infected.1
Conjunctival mucosa is the most commonly infected area, causing ophthalmia neonatorum. This usually presents at 5–14 days of age with conjunctivitis and often erythema and oedema of the eyelid. There is often a watery discharge, which may later become purulent. Untreated, most infections resolve spontaneously within the first few months of life, but corneal scarring has been reported.2
Chlamydia pneumonia develops in 7% of infants born to infected mothers.3 It typically occurs at 6 weeks of age but occasionally as early as the first week of life. A low grade fever, staccato cough and tachypnoea are typical. Treatment is with oral or systemic erythromycin for 14 days. Detection and treatment are important because longitudinal studies have shown an increased incidence of chronic cough and impaired lung function when compared with age-matched controls.4
Diagnosis is made by either culture or PCR of respiratory secretions, and by the detection of chlamydia IgM, which may be positive within 5 days.5 Chlamydia is an intracellular pathogen, so it is most readily isolated from specimens containing epithelial cells, such as those from the conjunctiva.
Rapid diagnosis by PCR is also possible from eye swabs. This is becoming the investigation of choice because the sensitivity and specificity are good.6
Although mild neutropenia had been noted during the early neonatal period, the current profound neutropenia was unexpected. As the possibility of an immunodeficiency existed a combined consultation with the immunology and infectious disease team and the haematologist was sought. The most likely explanation was thought to be either allo-immune or autoimmune neutropenia, both of which would resolve spontaneously. Also, neutropenia secondary to a congenital or acquired infection (for example, cytomegalovirus or chlamydia) or severe congenital neutropenia were considered. The potential causes of congenital neutropenia are numerous and listed in table 3. Regardless of the specific cause, it was decided to give daily injections of Granulocyte Colony Stimulating Factor (G-CSF) to treat the neutropenia and liposomal amphotericin to minimise the risk of an invasive fungal infection.
She was commenced on clarithromycin to treat a possible chlamydia infection, in addition to the liposomal amphotericin and G-CSF. She was noted to have a normochromic normocytic anaemia (table 2) and in view of this and the continued need for supplementary oxygen, a blood transfusion was given. The results of further investigations are shown in table 4.
Neutrophils are the predominant leucocyte in the peripheral blood, although a reversed differential with lymphocytes exists from 48 h of age until approximately 6 months. Neutrophils are an integral effector cell of innate immunity and as such, have a critical role in detecting and rapidly responding to invading micro-organisms, as well as initiating wound repair and healing.
Bone marrow production of neutrophils occurs in two stages; first the mitotic stage (myeloblasts, promyelocytes and myelocytes) and second the maturation phase (metamyelocytes, bands and polymorphs). Falling numbers of peripheral neutrophils are detected by tissue macrophages that produce IL-23 which ultimately acts on stromal cells to release G-CSF that stimulates haematopoietic stem cells to follow a maturation route that will end in the release of polymorphs into the circulation.7
Once activated, neutrophils become “sticky”. They then adhere to vascular epithelium and matrix, and move into adjacent tissue. Once in contact with an invading pathogen, the neutrophil discharges highly reactive oxidant intermediates leading to tissue and pathogen destruction and pus formation.
Neutropenia is classified as mild (>1.0×109/l), moderate (0.5–1.0×109/l), severe (0.2–0.5×109/l) and very severe (<0.2×109/l).12 The risk of severe infection does not increase until the neutrophil count falls below 0.5×109/l and varies according to the underlying cause and the duration of the neutropenia. The host is typically susceptible to gram-negative, streptococcal and fungal infection. Infections need to be aggressively treated with broad spectrum antibiotics and if necessary anti-fungals. The decision to use prophylactic antibiotics in neutropenia is based on both the clinical picture and the severity of the neutropenia. Co-trimoxazole is the prophylactic antibiotic of choice.8
The girl gradually improved during the next 4 days. Eight days after hospital admission the neutrophil count was 2.51×109/l (within normal limits) and 10 days after admission (8 days after starting G-CSF) it was 12.11×109/l.
Granulocyte colony stimulating factor (G-CSF) is a naturally occurring cytokine produced by macrophages, endothelium and other immune cells that acts directly on haemopoetic stem cells and thus increases the numbers of circulating neutrophils.
It is coded for on chromosome 17 and recombinant human G-CSF is synthesised in an E coli expression system.
G-CSF has been used for many years to treat children recovering from chemotherapy and a recent Cochrane review stated that there appeared to be a reduction in mortality in neonates with sepsis and associated neutropenia treated with G-CSF, although further research was needed.9
She was now symptom-free and started to grow along the 0.4th centile. The G-CSF was therefore discontinued, but within 48 h the neutrophil count had dropped to 0.69×109/l (fig 2) although her haemoglobin concentration remained satisfactory. She was therefore transferred to the specialist haematology unit to investigate the possibility of primary bone marrow disease. A bone marrow aspirate and trephine (fig 3) revealed a moderately cellular specimen with all cell lines represented. Granulopoeisis was slightly reduced but certainly present with maturation through to the neutrophil stage.
The most likely problem was thought to be with neutrophil destruction, either benign alloimmune or autoimmune neutropenia, but the results of neutrophil antibody tests, which could confirm these diagnoses, were outstanding. A primary bone marrow problem was considered unlikely and neutrophil maturation arrest (Kostmann syndrome) had been excluded.
She was discharged from hospital and her neutrophil count was regularly measured as an out-patient.
Neonatal alloimmune neutropenia has an incidence of less than 0.1% and occurs when maternal antibodies, produced in response to paternally inherited fetal neutrophil antigens, bind to and destroy fetal neutrophils.12 The mechanism is similar to Rhesus haemolytic disease of the newborn, but unlike Rhesus disease, neonatal alloimmune neutropenia commonly occurs in the first pregnancy.13 The diagnosis is confirmed by demonstration of maternal and baby neutrophil specific antibodies against paternally inherited antigens. The neutropenia may be severe but despite this infections are rarely severe. No specific therapy is indicated and the neutropenia resolves between 3–28 weeks (average 11 weeks). There is a high risk of recurrence for future pregnancies.
Primary autoimmune neutropenia, a relatively benign disorder, is characterised by neutrophil specific auto-antibodies. There is often severe neutropenia but as with allo-immune neutropenia, severe infections are rare and specific treatment with G-CSF and prophylactic antibiotics is not usually necessary. Diagnosis relies on finding neutrophil specific antibodies. The condition is self-resolving, often with complete recovery by an average age of 17 months from diagnosis.
At 3 months of age, she again developed the clinical features of pneumonia. The neutrophil count was 0.43×109/l. The neutrophil antibody test results were now available and excluded alloimmune and autoimmune neutropenia.
The absence of neutrophil antibodies does not wholly exclude the diagnosis of autoimmune neutropenia because in approximately 30% of cases no antibody is found. The combination of negative antibodies together with two episodes of sepsis in association with the neutropenia made the diagnosis in this case unlikely.
The pneumonia was successfully treated with antimicrobials and G-CSF. However, she was now failing to thrive (weight below the 0.4th centile) and further questioning revealed that since birth she had had frequent, large and foul-smelling stools. Stool microscopy showed numerous fat globules and faecal elastase was markedly reduced (42 µg/g). A sweat test excluded cystic fibrosis.
The results were diagnostic of fat malabsorption secondary to severe exocrine pancreatic insufficiency. This, together with the congenital neutropenia, suggested a diagnosis of Shwachman-Diamond syndrome.
Shwachman-Diamond syndrome (SDS) is a rare multisystem disorder characterised by bone marrow dysfunction, exocrine pancreatic insufficiency and bony abnormalities (classically metaphyseal chondrodysplasia). It is the second most common cause of exocrine pancreatic insufficiency after cystic fibrosis and affects 1 in 100 000–200 000 births.
It is an autosomal recessive condition caused by dysfunction of the Shwachman-Bodian-Diamond syndrome (SBDS) gene located on chromosome 7q11,14 of which 14 different mutations have been identified. This gene abnormality results in defective protein accumulation in the nucleosome, cytoplasm and sites of mRNA synthesis such as ribosomes.
Diagnosis is based on clinical grounds aided by the criteria used by Dror and Freedman.15 Bone marrow aspiration is often performed to exclude an infiltrative or primary bone marrow disease, and shows variable marrow cellularity and granulopoiesis with variable degrees of “left shift”. Molecular tests are now available for the different mutations and can be invaluable to remove diagnostic uncertainty in difficult cases. There is however poor genotype/phenotype correlation.
Although all patients with SDS have exocrine pancreatic involvement, diagnosed by two stool elastases <500 µg/g collected at a time when the patient is without gastrointestinal disturbance, there is a significant variation in phenotype, with some patients becoming pancreatic sufficient with increasing age.16 Unlike cystic fibrosis, the pancreatic ducts are preserved but there is paucity of acini and fatty replacement of the gland. Abdominal ultrasound and CT scan show a small abnormal pancreas mainly composed of fat, and can aid the diagnosis. Treatment is with pancreatic enzyme replacement therapy.
95% of patients with SDS will have either chronic or intermittent neutropenia. Anaemia, thrombocytopaenia and pancytopaenia have also been reported. Specific abnormalities of T and B cell numbers and function are also recognised, including low IgG or IgG subclasses, low percentage of circulating B lymphocytes, decreased in vitro B-lymphocyte proliferation and a lack of specific antibody production. These deficiencies are often overlooked and some patients may need antibody replacement therapy.17
The main adverse outcomes associated with SDS are:
bone marrow failure, in particular overwhelming sepsis secondary to neutropenia
transformation to myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML).
The neurophil count in SDS responds to G-CSF administration. There is no doubt that G-CSF availability and use has had a considerably beneficial effect on the mortality from infection in this condition. Two large case series of patients with congenital neutropenia syndromes treated with G-CSF have demonstrated a correlation between the incidence of the development of MDS and AML and the amount of G-CSF used.18 19 It is not clear whether this is due to a leukaemogenic effect of G-CSF, or to the fact that the more severely neutropenic and less responsive cases were more likely to transform anyway because of the biology of their underlying disease. Rather than using long-term prophylactic G-CSF routinely in order to maintain a numerically satisfactory neutrophil count, it seems prudent to tailor G-CSF use individually. Prophylaxis may be used in individuals demonstrating a propensity to infection, and therapeutic use together with antibiotic therapy employed for febrile neutropenic episodes.
The risk of malignant transformation is 24%, but is increased to 70% in a subgroup of patients with pre-existing pancytopaenia, myelodysplastic features and clonal cytogenetic abnormalities.20 Allogenic bone marrow transplantation (BMT) is the only chance of cure in these patients as conventional chemotherapy fails to regenerate normal haemopoiesis in the majority, but carries its own risks of complications and overwhelming sepsis. Evidence from two case series suggests that BMT in SDS can be well tolerated but the outcome is poor in those who have already transformed to AML/MDS.21 22 Ideally, the subgroup of patients identified as at risk to progression should be identified and transplanted pre-emptively.
Infants are often on the lower height and weight centiles, but the characteristic abnormality is metaphyseal chondrodysplasia. Recent studies have suggested that children with SDS may suffer from learning and behavioural difficulties.15
Genetic tests have confirmed the diagnosis of SDS. This patient is now on prophylactic antibiotics and enzyme replacement therapy. She is thriving with a weight on 0.4th centile and length 4 cm below the 0.4th centile.
Competing interests: None.