A 28-months-old boy was admitted with fever of five days and passing black colored stools one day prior to admission. The child was conscious, irritable, with petechial lesions over trunk and abdomen. Palms and soles were erythematous. He was febrile and had tachycardia, wide pulse pressure (50 mm Hg), and hepatomegaly. The child was diagnosed as a case of severe dengue based on a positive NS1 antigen, and positive dengue IgM, and clinical profile. The child was treated as per standard WHO protocol; he improved and was discharged home.

The child was readmitted on fifth day, with a diffusely swollen right knee. Movements were restricted. There was anemia ( Hb 8.2 g/dL), thrombocytosis (7,00,000 platelets/mm3), and elevated ESR (120 mm). Plain radiograph of right knee revealed widened joint space with normal surrounding structures. Serological examination was negative for anti-nuclear antibodies and Chikungunya IgM antibodies. Arthrocentesis of right knee revealed turbid fluid, with only five lymphocytes per mm3 without any organism on Gram stain and culture studies. Mantoux test was negative. The diagnosis of dengue arthritis was considered, against the post, viral reactive arthritis which usually involves hip joint. The child was treated with oral acetaminophen. At follow up after 2 weeks, the child was afebrile and playful without any pain or swelling in the right knee.

Dengue affects tendons, muscles, joints and bones. Polyarthralgia in dengue fever is known, but arthritis is rare [1,2]. Dengue and Chikungunya are arboviral infections transmitted by Aedes aegypti. They can be transmitted together in areas where both viruses co-circulate [3]. Most of the clinical and laboratory features of patients with chikungunya and dengue fever are similar. Arthritis is the predominant manifestation in patients with chikungunya fever compared to dengue fever [4]. Differentiating chikungunya with dengue fever is important as the former is a self-limiting acute illness whereas the latter has dreaded systemic complications. In view of relative well-being of a child, positive dengue IgM, negative serology for chikungunya, and normal arthrocentesis study, the diagnosis of dengue arthritis was made.

4. Kularatne SA, Gihan MC, Weerasinghe SC, Gunasena S. Concurrent outbreaks of Chikungunya and Dengue fever in Kandy, Sri Lanka, 2006-07: a comparative analysis of clinical and laboratory features. Postgrad Med J.