Utility of thick smears of bone marrow aspirate in pyrexia of unknown origin

To determine the diagnostic efficacy of Giemsa stained thick smear of bone marrow aspirate for evidence of malaria in febrile individuals in whom the diagnosis was otherwise unknown.

Descriptive case-series study.

This study was conducted at the Department of Medicine, Sandeman Provincial Hospital, Quetta, in the Balochistan province of Pakistan, between January 1994 and December 1998.

A total of 80 patients were included in the study, who presented with history of fever for more than 3 weeks with splenomegaly and pancytopenia. The bone marrow specimens of all these patients were examined. The bone marrow was aspirated from the posterior superior iliac spine. Three sets of smears were made. One set of thin smears was stained by Leishman's stain after air-drying and the second set of thin smears was air-dried, fixed with 97% methanol and later stained with 5% Giemsa stain. The third set of smears was a thick smear stained unfixed with 5% Giemsa stain. A temperature of 37 degrees C and a pH of 7.2 was maintained during the staining process. The presence of malarial parasite in the bone marrow was determined. Besides, the degree of megaloblastic change in erythroid series and the bone marrow cellularity were evaluated. The results obtained were recorded and statistically analyzed.

Of the 80 bone marrows examined, 32(40%) showed the presence of malarial parasites, 19(23.75%) showed haematological malignancies, 16(20%) showed bone marrow suppression while 12(15%) showed megaloblastic changes. One (1.25%) case showed Leishman-Donovan bodies. Out of 32 cases showing the presence of malarial parasite in bone marrow, only 5(15.6%) revealed parasites, i.e. Plasmodium falciparum gametocytes on thin smear while 32(100%) cases showed Plasmodium falciparum trophozoites and gametocytes on thick smear. The ratio was 1:6.4. These 32 patients were divided into two groups, one group having mild anaemia (>8 g/dL) and the other severe anaemia (Hb<8 g/dL). In this study 20 patients had mild and 12 had severe anaemia. Megaloblastic changes were seen in 15 cases. Hypocellularity was seen in 3 patients with falciparum malaria while 28 showed normocellularity. The marrow was hypercellular in one patient.

In patients presenting with prolonged fever, splenomegaly and pancytopenia, the Giemsa stained thick smear of bone marrow aspirates for evidence of malarial parasites was far superior to thin smear in diagnosing Plasmodium falciparum malaria.