Chikungunya fever (CF) is a viral disease whose transmission occurs through vector females of Aedes aegypti and Aedes albopictus mosquitoes infected by the Chikungunya virus (CHIKV). There are reports of outbreaks in Europe, the Americas, Asia, Africa, and Oceania [1].

Approximately 60% of patients with CHIKV infection progress to chronic arthritis [2]. In these cases, joint limitations can persist for up to five years after infection [3] and are associated with permanent sequelae [4]. After an incubation period of three to seven days, patients may experience fever, skin rash, myalgia, and arthralgia. The disease becomes chronic when the arthralgias persist for more than three months. The literature shows that a small portion of patients with chronic CF and severe polyarticular forms develop rheumatoid arthritis (RA) [5] or other forms of arthritis, including psoriatic arthritis (PsA) [6].

Conventional radiology is still a first-line exam in the investigation of rheumatological diseases. However, the method is not as sensitive as MRI or US in showing early bone and soft tissue changes. Although US has limitations in bone evaluation, together with Doppler it can identify early signs of enthesitis or organ-enthesis involvement [7]. Conventional MRI, in turn, is useful for diagnosing bone complications such as marrow edema and erosions as well as soft tissue involvement [8].

The pattern of involvement of the hands and wrists by CF is very similar to that found in RA, and it is characterized by symmetrical and bilateral involvement of the metacarpophalangeal and proximal interphalangeal joints, tenosynovitis, subcutaneous edema, and bone changes, such as marrow edema and erosions [9].

Although there have been several reports of developing RA, to our knowledge, there are few descriptions of post-CF PsA. Mathew et al. [5] investigated 1396 individuals with CF and concluded that only 2.5% of patients developed PsA. Thus, our report is valuable due to the scarcity of cases, and it features an imaging presentation typical of peripheral spondyloarthropathy secondary to arbovirus infection.

A 49-year-old man had a fever (101.30°F/38.5°C) for approximately ten days and exhibited persistent signs of polymyalgia and polyarthralgia. He used dipyrone and oral hydration to reduce the fever, and his musculoskeletal symptoms partially improved. Serologies for CHIKV were positive for IgM (51; normal value: 9). Subsequently, a skin rash appeared, and polyarthralgia associated with edema of the hands, wrists (Figure 1), elbows, knees, and feet worsened. Two months later, he was evaluated in an outpatient rheumatology clinic at a university hospital in Rio de Janeiro, Brazil. He continued to experience polyarthralgia and edema in the metacarpophalangeal and interphalangeal joints, especially of the left hand. Erythematous scaling and itchy skin lesions were also noted in the anterior medial region of the scalp on physical examination. At the time, the patient was not taking any known medication that could precipitate psoriasis. He also denied any preceding emotional stress (at least two months prior to the appearance of the skin lesion). The patient had never had any episode of psoriatic skin lesions. The patient was hypertensive, using enalapril 20 mg/day, and was an abstainer, nonsmoker, and physically active. He denied allergies and blood transfusions and had an up-to-date vaccination schedule. His father had PsA. One maternal aunt had multiple sclerosis, and another had ankylosing spondylitis.

The rheumatologists prescribed meloxicam 15 mg/day and prednisone 20 mg/day after discussing the case. The patient returned the following month with little clinical improvement, and methotrexate 15 mg and folic acid 5 mg were started after verification of the laboratory tests.

After starting the medication, he was followed up on an outpatient basis and remained asymptomatic. However, the patient stopped medication on his own, and after two years and four months he returned to the outpatient clinic with symptom recrudescence. After that, the joint pain returned, but the psoriatic skin lesions did not. He was re-evaluated with US and MRI.

Written consent was obtained from the patient to be evaluated at the rheumatology outpatient clinic and the radiology department of a university hospital in the city of Rio de Janeiro, Brazil.

There were no changes in the patient’s complete blood count: C-reactive protein 13 mg/L (normal index: up to 3 mg/L), fibrinogen 340 mg/dL (normal index: 200–400 mg/dL), and normal levels of transaminases and electrolytes (sodium and potassium). The nonreactive immunological tests included the following: antinuclear factor (ANA), antibodies against citrullinated peptides (ACPA), rheumatoid factor (RF), and cytoplasmic antineutrophil antibodies (ANCA). Serological tests for HIV and hepatitis B and C were nonreactive; CHIKV IgM and IgG were reactive; and HLA-B27 was negative.

The equipment used was a Toshiba US, model Aplio XG, with a 7–18 MHz multifrequency probe, in B mode and with power Doppler (pulse repetition frequency 750 Hz, low wall filter and gain adjusted just below the appearance of the artifacts).

The MRI scans were performed in a Siemens model Avanto, 1.5 T high-field scanner. The image acquisition protocol had the following sequences: protonic density (PD) with fat saturation in the axial, sagittal, and coronal planes and T1 pre- and post-contrast fat saturation in the axial plane.

The US and MRI scans showed signs of arthritis in the wrist and metacarpophalangeal joints of both hands. There was also tenosynovitis of all extensor compartments, digital flexor tenosynovitis (Figure 2 and Figure 3), and signs of classical enthesitis due to thickening of the digital extensor entheses and functional enthesitis (Figure 4, Figure 5, Figure 6) due to peritendinous extensor thickenings. Vascular hyperflow was observed by power Doppler (Figure 4) at several sites of inflammation, paramagnetic contrast enhancement of the distended sheaths, and functional enthesitis sites. Focal bone edema was identified as an indirect sign of enthesitis at the base of the left third metacarpal associated with signs of inflammation of the extensor carpi radialis brevis.

The authors present an unusual complication of CF suggested by clinical and imaging findings. US and MRI were also essential during the treatment follow-up.

According to the Classification Criteria for Psoriatic Arthritis (CASPAR) [10], to confirm the diagnosis of PsA, it is necessary to have an inflammatory joint disease and at least a three-point score in the other categories. The patient had a five-point score due to scalp psoriasis (two points), family history (one point), negative RF (one point), and dactylitis (one point). As reported in other literature cases, these signs and symptoms appeared immediately after CF infection, and the disease regressed with methotrexate therapy [5].

The patient’s age and gender profiles disagree with the literature, which describes a predominance in women over 45 years old who are at risk for musculoskeletal complications in CF [11]. Among the usual manifestations of CF, the presentation of only fever, polymyalgia, polyarthralgia, and skin rash and the high levels of C-reactive protein are in accordance with the literature [12].

The US and MRI scans showed several signs of involvement, with characteristics of spondyloarthropathy: dactylitis due to flexor tenosynovitis, classic enthesitis in distal extensor insertions, functional enthesitis due to peritendinous extensor thickening adjacent to the metacarpophalangeal and interphalangeal joints, and metacarpal marrow edema adjacent to the insertion of an extensor tendon.

After the 2015–2016 CF outbreak in Rio de Janeiro, Brazil, our group [9],[13] reported wrist/hand and ankle ultrasound changes. The authors highlighted bilateral synovitis and tenosynovitis as relevant findings for the diagnosis of musculoskeletal complications. However, in this case report, the existence of several signs of very intense enthesitis and flexor tenosynovitis in the imaging exams raised the suspicion of some other disease associated with CF.

There are two types of entheses according to function and location: fibrous and fibrocartilage. The most common fibrocartilage is found in the apophyses and epiphyses of long bones, short bones of the hands and feet, and several ligaments in the spine. Fibrous entheses are found in the metaphyses and diaphyses of long bones. Fibrocartilaginous entheses are those affected in spondyloarthropathies and altered in the US and MRI exams of the reported case [14], [15].

Functional enthesis is another essential concept to understanding our imaging findings. In specific locations where the tendon deflects or rubs against a bone surface, there are sesamoid (tendinous) and periosteal fibrocartilages. This patient had intense digital peritendinous extensor inflammatory thickenings, which are explained by these functional enthesis impairments [16],[17].

Dactylitis is one of the main features of psoriatic arthritis and is present in 40% of cases. The main finding is digital flexor tenosynovitis, that is, distention of the fibrous sheaths, which also existed in the reported case [18].

Clinical recognition of early-stage PsA is challenging when the disease affects only the peripheral joints. Despite the efficiency of CASPAR in identifying patients with less than one year of symptom onset (early psoriatic arthritis) [19], peripheral PsA remains a challenge for rheumatologists [20]. In our case, imaging helped detect the entheseal manifestations of the disease, suggesting alternative diagnoses in CF patients.

With the resurgence of CF epidemics worldwide, managing chronic arthritis has become an enormous challenge for rheumatologists. It is essential to follow these chronic cases and to identify the progression to other forms of arthritis, such as PsA. Imaging exams have become indispensable for the diagnosis and management of these complications.