Myelofibrosis in young pygmy goats

Marked widespread myelofibrosis occurred in 11 of 16 pygmy goats from seven litters (two sires and four dams). Sires and dams were haematologically normal. Clinical histories of affected goats included lethargy, poor weight gain, and pale mucous membranes. Anaemia and neutropenia resulted in death within 6–12 weeks of age. A diagnosis of myelofibrosis was confirmed histologically in nine goats and was based on clinical signs and history in the remaining two littermates. The marrow of long bones was most severely affected with proliferation of well-differentiated fibrocytes and abundant collagen deposition. There was bone marrow megakaryocyte hyperplasia, individual megakaryocyte necrosis, megakaryocyte emperipolesis of haematopoietic cells, and clusters of degenerative megakaryocytes were present adjacent to some fibrotic foci. Prominent areas of extramedullary haematopoiesis were present in many organs but were most consistently observed in liver, thymus gland, and lymph nodes. The aetiopathogenesis of marrow fibrosis was not determined; however, clinical, haematological, and/or bone marrow morphological features in the goats were similar to findings in anaemic dogs with congenital pyruvate kinase deficiency or in human beings with myelofibrosis due to dysmegakaryocytopoiesis.