Table 2.

Systematic histological bone marrow findings, which aid in the discrimination of chronic myeloproliferative neoplasms

Histological findings			Polycythemia vera	Essential thrombocythemia	Primary myelofibrosis
					Cellular phase	Fibrotic stage
Increased cellularity				++	+++++	++
Granulopoiesis	Increased		+++++	++++	0
	Left shift	++++	+++++	+++	++
Erythropoiesis	Increased	+++++	+	+	0
	Left shift	+++++	+	++	+
Megakaryopoiesis	Increased	++++	+++++	++++	+++
	Size	Small	+++	0	+++	+++
		Medium	+++	++	++	++
		Large	+++	+++	++++	++
		Giant	++	+++	++	+
	Topography	Endosteal translocation	++	++	+++	+++
	Cluster size	Small (≥ 3)	++	++	++++	++++
		Large (>7)	+	0	+++	+++
	Cluster type	Dense	+	0	+++	++++
		Loose	+++	+++	++++	++
	Nuclei shape	Hypolobulation	++	+	++++	++++
		Hyperlobulation	++++	++++	++++	+++++
	Maturation defects		0	0	++++	+++++
	Naked nuclei		+++	+++	++++	+++++
Fibers	Increased reticulin		++	0	++++	+++++
	Increased collagen		0	0	0	+++++
Osteosclerosis			0	0	0
Iron deposits			0	+++	++	+
Lymphoid nodules present			++	0	++	+

Semi-quantification: 0 usually absent; + rare; ++ slight; +++ moderate; ++++ manifest; ++++ overt

Adapted from: Thiele J, Kvasnicka HM. The 2008 WHO diagnostic criteria for polycythemia vera, essential thrombocythemia and primary myelofibrosis