Autoimmune neutropenia, which primarily occurs in infants, is characterized by antibodies that destroy neutrophilic white blood cells, increasing the risk of infection.
Primary autoimmune neutropenia (AIN) is an autoimmune disorder first reported in 1975 that primarily occurs in infancy. In autoimmune neutropenia, the immune system produces autoantibodies directed against the neutrophilic protein antigens in white blood cells known as granulocytic neutrophils (granulocytes, segmented neutrophils, segs, polysegmented neutrophils, polys). These antibodies destroy granulocytic neutrophils. Consequently, patients with autoimmune neutropenia have low levels of granulocytic neutrophilic white blood cells causing a condition of neutropenia. Neutropenia causes an increased risk of infection from organisms that the body could normally fight easily.
Who is Affected?
Primary autoimmune neutropenia has been reported as early as the second month of life although most cases are diagnosed in children between 5 and 15 months of age. Girls have a slightly higher risk of developing AIN than boys. In neutropenia discovered at birth or shortly after birth, a diagnosis of allo-immune neutropenia (from maternal white blood cell antibodies passively transferred to the infant) is more likely.
Neutropenia
In infants neutropenia is defined by absolute neutrophil counts less than 1000/uL. After the first year of life neutropenia is defined by absolute counts less than 100/uL. Neutropenia may be primary in which is the only blood abnormality seen. In secondary neutropenia, other primary conditions occur, including other autoimmune diseases, infections, and malignancies. Neutropenia is considered chronic when it persists for more than 6 months.
Symptoms and Disease Course
Neutropenia, which may be discovered on routine blood tests, typically causes benign infections even when the condition is severe. Ear infections (otitis media) are the most common infection seen in autoimmune neutropenia and typically infection responds to antibiotic treatment alone. Infections associated with primary AIN are usually mild and limited, including skin infections such as impetigo, gastroenteritis, upper respiratory tract infections, and ear infections. Rarely, cellulitis and abscesses may occur.
Studies of children studied for up to six years showed that most cases of autoimmune neutropenia resolved spontaneously after a median of 17 months. In 80 percent of patients, neutropenia persisted for 7 to 24 months.
Diagnosis
Patients with autoimmune neutropenia are diagnosed on the basis of blood tests showing neutropenia and the presence of granulocyte-specific antibodies. In some cases, tests for granulocyte-specific antibodies need to be repeated several times before a positive result is seen. Bone marrow aspiration, if performed, is typically normal or it can show increased cell production with a variably diminished number of segmented granulocytes.
As association with prior parvovirus B19 has been made but this hasn’t been confirmed. Similar to the platelet deficiency idiopathic thrombocytopenic purpura, vaccines are suspected of triggering this disorder.
Treatment
Treatment consists of corticosteroids to reduce autoantibody production, antibiotics to prevent infection and granulocyte colony-stimulating factor (G-CSF) to temporarily increase neutrophil counts. In cases of severe infection or the need for surgery, intravenous immunoglobulin therapy may be used.
Resources:
Juergen Bux, Georg Behrens, Gudrun Jaeger, and Karl Welte, Diagnosis and Clinical Course of Autoimmune Neutropenia in Infancy: Analysis of 240 Cases, Blood Vol 91, Jan 1998: 181-186.
Susumu Inoue, Autoimmune and Chronic Benign Neutropenia, eMedicine from WebMed, June 13, 2006, accessed Sept 29, 2006.
