A 24-year-old man with a 12-month history of pain and swelling in his left ankle.
History of the present illness
The patient was referred to our unit with a 12-month history of worsening pain and swelling in his left ankle. There was no history of trauma. He experienced nocturnal pain and morning stiffness, with little impact on his physical performance or daily activities. He reported relief of symptoms with nonsteroidal antiinflammatory drugs. Before referral, plain radiography and magnetic resonance imaging (MRI) had been performed and considered inconclusive. Radiographic films showed preserved joint spaces at the hindfoot and a blurred area in the upper facet of the talus (results not shown). With MRI, an altered trabecular bone pattern of the talus was evident, with a focal lesion that was hyperintensive in T2-weighted and STIR sequences (Figure 1). There was a moderate synovial enlargement of the ankle joint, without any specific lesion. Taken together, the findings from the two imaging studies suggested chronic arthritis of the ankle with initial erosive involvement.
His medical history was positive for past infectious mononucleosis.
Family and social history
The patient worked as an electronic engineer and did not practice sports regularly. He had an aunt diagnosed with psoriasis. His father had died of gastric lymphoma. Otherwise, his family history and his epidemiologic background were unremarkable.
Review of systems
Additional signs or symptoms, including fever, back pain, skin involvement, and bowel or eye disease, were absent, and no other joints were sensitive.
General examination showed a well-built young man with normal vital signs. He had a regular heart rhythm with no murmurs, his lungs were clear, and he had a soft abdomen without either organomegaly or masses. There were no visible skin lesions. Joint examination revealed a sensitive and swollen left ankle, with little impairment in range of motion. Mobility of the spine as well as at rest of peripheral joints was preserved. The modified Schober test was 54 mm and Fabere's maneuvers were not painful.
Laboratory evaluation and ancillary studies
Blood tests are shown in Table 1. In brief, the white blood cell count was 8.84 × 109/liter and the C-reactive protein level and erythrocyte sedimentation rate were within normal values; while screening for rheumatoid factor, HLA–B27 antigen, antinuclear antibodies, as well as a tuberculin skin reaction showed negative results.
With high-frequency sonography, we could confirm the existence of a moderate effusion in the ankle joint, bulging to the anterior and lateral compartments. No alterations were found at tendon sheets. A mild thickening of the synovial membrane was associated with a grade 1 power Doppler signal (0–3 scale). A slightly turbid effusion was aspirated by ultrasound-guided puncture of the joint. The synovial fluid characteristics are summarized in Table 2.
Table 2. Synovial fluid characteristics
Synovial fluid tests
White blood cells, × 109/liter
Lactate dehydrogenase, units/liter
Ongoing at the time of diagnosis, finally negative
A young man with well-tolerated chronic monarticular arthritis showing initial bone involvement in image studies.
The diagnosis of true chronic monarthritis is relatively easy to approach because most of the inflammatory rheumatic diseases spread with time to other joints or anatomic sites, and are therefore rarely associated with the syndrome (1). In contrast, most cases of chronic monarthritis are generally precipitated by local factors, such as infections or structural lesions (2–4) (Table 3).
Table 3. Differential diagnosis of chronic inflammatory monarthritis
Nongonococcal septic arthritis
Lyme disease and other spirochetal infection
Reflex sympathetic dystrophy
Calcium apatite crystals
Monarticular presentation of an inflammatory joint disease
Hemarthrosis (coagulopathy, use of warfarin or dicumarinics, etc.)
Joint structural damage
Immediate diagnostic procedures to perform are plain radiographies and synovial fluid aspiration, which also allow assessment of severity (2, 5). In brief, radiographs are usually positive in osteoarthritis, crystal deposition, fractures, osteonecrosis, erosive arthritis, bone or marrow tumors, and adjacent osteomyelitis. MRI is often performed as a routine technique due to its high anatomic resolution and its sensitivity to assess soft tissues, as well as chondral and bone alterations. Most of the conditions associated with monarticular arthritis can be diagnosed combining both image techniques.
Similarly, synovial fluid analysis is of utmost value (6). In this regard, the microscopic examination of the fluid provides a straightforward method for the diagnosis of crystal arthropathies. Cell counts lower than 1,500 leukocytes per mm3 are typical of mechanical injuries, such as internal derangements, or overload associated with osteoarthritis. Fractures and tumors may yield an increased erythrocyte count (5). Finally, cultures as well as indirect microbiologic tests should be done, since infections can frequently account for unexplained monarthritis, even when noninflammatory effusions are drawn.
In the present case, the course had been mild and the synovial effusion was clearly noninflammatory. On the other hand, bone involvement appeared undeniable, and the occurrence of nocturnal pain was intriguing. Taking all of these facts together, we considered several diagnostic possibilities, as follows.
Joint infections are more often suspected if the host is debilitated. Either opportunistic or slow-growing microorganisms can cause chronic monarthritis. The history is often positive for exposure, penetrating wounds, a predisposing condition such as diabetes mellitus, or a preceding episode of fever and malaise. Nonetheless, mycobacterial and fungal infections may provoke a characteristically nonremitting monarthritis in healthy individuals (7, 8). Tuberculosis is highly prevalent in most developed countries, and it can target joints in the absence of other evident focus. It is therefore advisable to perform a tuberculin skin test as part of the routine evaluation of chronic monarthritis. Atypical mycobacteria, Candida, and coccidiomycosis can produce a similar syndrome. Since mycobacteria and fungi seldom grow in synovial fluid cultures, tissue samples would have been needed to completely rule out these pathogens.
The absence of typical systemic signs of infection is relatively frequent, so it does not provide evidence against the diagnosis. What was relatively unusual was the lack of synovial thickening generally associated with chronic infections.
Most bone conditions yield definite radiographic or MRI findings, particularly in the case of long-lasting symptoms. In this regard, osteochondritis, fractures, Paget's disease, or aggressive tumors could be discarded. However, some features in this case supported primary bone involvement progressing to the adjacent joint. Positively, the synovial enlargement was small as compared to the bone lesion. Also noteworthy was the fact that a single bone was affected, while erosive joint diseases very likely spread to both sites of the joint. Finally, joint cartilage was spared.
Inflammatory joint diseases
As discussed, rheumatic diseases causing chronic monarthritis are expected to yield an inflammatory effusion and synovial membrane thickening. Acute-phase markers, anemia, or other systemic alterations associated with inflammatory disorders were not found. On the other hand, our patient had a characteristically inflammatory discomfort, predominating at night and early in the morning. Polyarticular diseases such as rheumatoid arthritis can present with monarticular involvement, although they are not likely to remain restricted to one joint after several months (9). Of all of the inflammatory joint diseases, only psoriatic arthritis seemed plausible. In this regard, the patient had a positive family history for psoriasis, albeit not affecting a first-degree relative. Additionally, psoriasis, unlike rheumatoid arthritis, may provoke early central erosions with cartilage preservation. However, it was only a remote possibility, considering that other radiographic or skin and nail typical lesions were absent (9). Of note, in two recent epidemiologic studies carried out in Norway, psoriatic arthritis affected a single joint in only 5–7% of cases (10, 11).
Primary synovial conditions
Pigmented villonodular synovitis can take a similar course to our patient's. A precipitating trauma is found in 50% of cases, but the rest do not show any particular predisposing factors. The disease is usually slowly progressive so that it can present as long-lasting monarticular swelling. The location at the ankle joint is not uncommon (12). Usually, there are sprouts of synovial membrane proliferation, resulting in focal bone and cartilage involvement. All of these facts would strongly have supported the diagnosis in this case, but the characteristic MRI findings were lacking (13).
Synovial osteochondromatosis and lipoma arborescens produce considerable synovial growth that impairs range of motion. However, pain is hardly noteworthy. Moreover, these conditions are associated with typical findings in routine radiographs and MRI, respectively (13, 14). Up to 25% of cases of synovial chondromatosis are not calcified and may yield nonspecific radiographies. In these cases, soft tissue masses can be evident, as well as joint space widening with or without focal erosions. Subchondral bone density is typically preserved, except when secondary osteoarthritis develops. Arthrograms reveal characteristic filling defects, which allow diagnosis (12).
Internal derangement, loose bodies, or overload
These mechanical injuries looked very improbable in regard to the patient's clinical history. Usually they are associated with a rapid onset of symptoms and load- dependent pain and swelling. Moreover, they lead to the development of secondary osteoarthritis with time.
DIAGNOSIS AND SUBSEQUENT COURSE
At this point, we considered performing a synovial biopsy as the next diagnostic step, and it would have been the method of choice to rule out or confirm infection. On the other hand, there were further image studies that could possibly shed light on this case. Magnetic resonance arthrography is more sensitive than conventional MRI in the assessment of intrajoint pathology and is being widely used in the evaluation of ankle lesions, including ligamentous injuries, loose bodies, synovial disorders, and osteochondral lesions of the talus (15). However, helical computed tomography (CT) is clearly superior to MRI in the definition of the bone structure (16), and we decided, in coordination with the musculoskeletal radiologists of our institution, on this study. The CT scan showed a solitary dense lesion surrounded by an osteolytic halo and a ring of reactive sclerosis from the adjacent bone. It was located beneath the upper facet of the talus. A focal loss of cortical bone could be observed in contact with the joint capsule (Figure 2). The central round-shaped lesion was a typical nidus, and the image was diagnostic for osteoid osteoma. Therefore, no additional studies were necessary. The patient was thereafter referred to the Radiology Department for treatment with radiofrequency ablation.
THE PATIENT'S COURSE
Under general anesthesia and CT guidance, a Cool-tip 10-mm radiofrequency electrode was applied to the lesion, locally reaching 90°C for 12 minutes at the target site. Total pain relief was achieved within the next 24 hours of the procedure, and no complications were noticed. He was discharged two days after therapy, walking normally.
Osteoid osteoma can be difficult to diagnose, particularly when located inside joints (17, 18). Although tumors are a frequent cause of chronic monarthritis, osteoid osteoma usually targets corticodiaphyseal or metaphysary sites of long bones. Of note, the location at the ankle and feet is typical for this tumor, with an estimated incidence of 2–11% of all tumors found at this anatomic region. It should, therefore, be regarded as a potential diagnosis in all cases of chronic foot pain, as has been recently underlined (19). Intraarticular osteoid osteoma may mimic inflammatory joint diseases (20). Indeed, the tumor is widely recognized for causing nocturnal pain characteristically relieved with aspirin. Likewise, osteoid osteoma may provoke joint swelling in those cases where the lesion is in proximity to the bony end, like in our patient.
The typical appearance of osteoid osteoma on radiographs facilitates diagnosis. However, the nidus formation can be hidden in standard joint views, as in the case we describe, in which it was taken for an erosive lesion (21). As it has been established, the degree of bony sclerosis and the maturation of the lesion are highly variable, mostly in relation to disease duration.
Also, MRI studies can be misleading. No doubt a front-line element in the diagnostic evaluation of chronic monarthritis, MRI is definitely less sensitive and specific than CT in defining the typical central calcified nucleus of osteoid osteoma. Particularly in iuxtaarticular localizations, secondary signs such as reactive synovitis or hyperostosis may be overestimated by MRI (17–19). Shukla et al recently published a 9-case series of foot osteoid osteoma. Four tumors were located in the calcaneus, 1 in the talus, 2 in the phalanges, and 2 in the metatarsals. One lesion was intraarticular. Interestingly, all cases of hindfoot osteoid osteoma showed normal radiograph images, while the CT scan identified 8 of 9 tumors, including all of the hindfoot lesions. A nidus was evidenced in 6 of 9 cases by MRI, the technique failing to identify the tumor located in the talus (19).
Most of the monographies enlisting disorders associated with chronic monarthritis fail to mention osteoid osteoma (1–4). In this regard, it may be important to consider people ages <30 years as a particular patient group (19). Positively, principal conditions to rule out in older patients are infection, crystal-induced arthritis, sarcoidosis, or a monarticular presentation of polyarticular diseases (Table 2), whereas in young adults, bone tumors, along with leukemia, lymphoma, and neuroblastoma, are not rare.
Thermal ablation with radiofrequency is an increasingly used therapeutic option for symptomatic osteoid osteoma, as well as for a variety of musculoskeletal conditions (22). It is a minimally invasive CT-guided percutaneous procedure based on the application of a high-frequency alternating current through an electrode placed into the lesion. The current provokes a heat-induced necrosis of the nidus, with an estimated primary and secondary success rate of 97% and 100%, respectively, and minimal morbidity. Most patients are symptom free within one week and there has been no report of significant early or late complications to date (23, 24).
In summary, we describe a case of osteoid osteoma initially misdiagnosed as inflammatory joint disease due to its atypical intrajoint location. We should regard location and age as key factors pointing to particular causes of monarthritis. As illustrated here, intraarticular osteoid osteoma needs to be taken into consideration as a cause of chronic monarticular syndromes of the ankle and foot in young adults.
Intraarticular osteoid osteoma of the ankle.
All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Sanchez-Pernaute had full access to all of the data in the study and takes responsibility for the integrity of the data.
Study conception and design. Sanchez-Pernaute.
Acquisition of data. Gonzalez-Martin, San Jose, Sanchez-Pernaute.
Analysis and interpretation of data. Gonzalez-Martin, Sanchez-Pernaute.