The disease is identified on the basis of the clinical picture. The diagnosis should be serologically confirmed in order to avoid unnecessary investigations and treatment attempts.
Pogosta disease may be associated with chronic joint manifestations.
Epidemiology
The aetiological agent is Sindbis virus (family Togaviridae, genus Alphavirus), which is spread by late summer mosquito species. The disease can be found in most of Finland in August-September.
Some tens or hundreds of cases are diagnosed in Finland annually. From time to time, outbreaks of as many as several thousands of cases occur.
Sindbis virus causes clinically similar diseases in nearby geographical areas, in Sweden (Ockelbo disease) and Russian Karelia (Karelian Fever).
Elsewhere in the world, there are also other Alphaviruses that cause infections with joint symptoms. The most significant is the chikungunya virus which can cause a disease with a much more severe clinical picture than that of Pogosta disease Viral Diseases in Warm Climates.
Symptoms
The typical clinical manifestation consists of arthritis, itching maculopapular rash in the trunk and limbs (pictures 12, muscle pain and mild fever.
Other possible symptoms are fatigue, headache and nausea.
Usually polyarthritis (typically 3-5 joints), especially affecting ankle, finger, wrist and knee joints. The joint symptoms usually co-occur with other symptoms.
Arthritis typically manifests as tenderness in movement, ache and oedema.
Diagnosis
Time of the year: the majority of acute cases of Pogosta disease in Finland occur in late summer, but some cases have been diagnosed as early as in June.
Acute disease is not encountered during the winter in Finland.
Prolonged articular symptoms may be found even after the epidemic season.
When Pogosta disease is clinically suspected, the diagnosis should be confirmed with serology.
Serodiagnosis is based on measuring IgG and IgM antibodies to Sindbis virus (SINV) using EIA.
Positive IgM-result or a rise in SINV antibody titre (1-week interval between samples) is decisive for the diagnosis.
If there is less than a week from the onset of symptoms, a negative antibody result does not rule out the infection, and a second sample is required.
The majority of cells in synovial fluid are mononuclear - or polynuclear; the total white blood cell count is usually < 10 000.
Basic blood count with platelet count and CRP are usually normal.