Combined Megaloblastic and Sideroblastic Anemia in an Infant Fed With Goat’s Milk
On examination, he was very pale, sedated and intubated with fever, tachycardia, hypotension and increased rate of breathing. His lab results revealed normocytic (mean corpuscular volume=75.9 fL) anemia (hemoglobin, 1.8 g/dL), high red cell distribution width of 32.8%, thrombocytopenia and leukocytosis, along with metabolic derangements. Both the serum folate level (<2.0 ng/ml) and vitamin B6 level (13.2 nmol/L) were low. Serum iron studies and vitamin B12 level were within normal limits. Persistent pancytopenia prompted a bone marrow biopsy, which showed megaloblastic changes in the erythroid and myeloid lineage with ring sideroblasts (<15% of the erythroid cells) (Figs. 1A–D). Serum copper and lead levels were in the normal range.
On the basis of the history and clinical and laboratory findings, a diagnosis of combined megaloblastic and sideroblastic anemia was made for this patient. The normocytic red cell indices noted were likely due to the concomitant presence of a macrocytic anemia from folate deficiency with a microcytic anemia resulting from the vitamin B6 deficiency. This is supported by the increased high red cell distribution width reflecting marked anisocytosis.
To our knowledge this is the first reported case of a goat’s milk induced combined vitamin B6 and folic acid deficiency in an infant exclusively fed on goat’s milk. Goat’s milk is a very poor source of folate (6 μg/L) compared with human milk and cow’s milk.1 It has been well established that infants receiving goat’s milk exclusively in their diet are likely to develop megaloblastic anemia as a manifestation of folate deficiency.2
However, our patient presented with a very interesting and unusual finding of sideroblastic anemia, due to a concomitant microcytic anemia related to vitamin B6 deficiency. Sideroblastic anemia commonly occurs due to copper deficiency,3 however, it is generally rare in term infants. Moreover, in our patient, copper levels were normal, so the sideroblastic anemia was thought to be exclusively due to vitamin B6 deficiency. There are very few studies reporting that goat’s milk is deficient in vitamin B6 resulting in vitamin B6 deficiency.4 The patient’s history and laboratory studies did not support other etiologies, and there was no history of medication use, such as isoniazid. Following cessation of goat’s milk and gradual introduction of oral formula feeds, the patient’s symptoms related to the folate and vitamin B6 deficiencies resolved. In addition, the abnormal blood counts seen on presentation resolved (Table 1). With the resolution of the symptoms and blood count abnormalities, the possibility of a congenital or inherited sideroblastic anemia was very unlikely in this patient.