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Q1: What is the most probable diagnosis?
The most probable diagnosis in this patient is adult onset Still's disease. This patient had fever for more than a week, rash, arthralgia, and leucocytosis fulfilling the four major criteria for the diagnosis of adult Still's disease. He also had minor criteria (lymphadenopathy, sore throat, liver dysfunction, and negative rheumatoid factor, and antinuclear antibodies), thus confirming the diagnosis. The investigations excluded infections, malignancies, and rheumatic diseases. The markedly raised serum ferritin concentration strengthens the diagnosis of adult onset Still's disease.
Adult Still's disease is one of the febrile disorders of unknown aetiology characterised by typical spiking fever, evanescent rash, and involvement of various organs.1
Box 1: Criteria for adult onset Still's disease
- Fever of 39°C or higher, lasting one week or longer.
- Arthralgia lasting two weeks or longer.
- Macular or maculopapular non-pruritic salmon pink eruption usually appearing during fever.
- Leucocytosis (10 × 109/l or greater) including 80% or more of granulocytosis.
- Sore throat.
- Lymphadenopathy and/or splenomegaly.
- Liver dysfunction.
- Negative rheumatoid factor and antinuclear antibodies.
The diagnosis especially in the early stages of the disease is difficult because of the lack of specific clinical, laboratory, and histological features. Most patients will not present all the characteristic features such as high fever, joint symptoms, rash, and leucocytosis. The delay in the diagnosis may result in prolonged and unnecessary investigations or in unwarranted treatment. Though various diagnostic and classification criteria have been proposed, Yamaguchi criteria have the highest sensitivity (96.2%) and specificity (92.1%).2
The preliminary criteria for the classification of adult onset Still's disease involve four major and four minor criteria (box 1).2
The diagnosis of adult onset Still's disease requires five or more criteria including two or more major criteria and needs exclusion of infections, malignancies, and rheumatic diseases.2Increased concentrations of ferritin have not been included in the criteria list, but are recognised as an important discriminator.1 It has been suggested in many reports that increased serum ferritin of greater than 4000 μg/l is a useful test to aid in the diagnosis of adult onset Still's disease.3Besides being an important tool it also helps to monitor disease activity and guide decisions about treatment.4 Other causes with high serum ferritin are listed in box 2, but the values of serum ferritin in these conditions rarely exceed 5000 μg/l.5-7
Box 2: Causes of markedly raised serum ferritin
Malignancies, such as acute and chronic leukaemias, malignant lymphoma, melanoma, germ cell tumour, and neuroblastoma.
Acute liver necrosis.
Adult onset Still's disease.