Coccidiomycosis infection of the patella mimicking a neoplasm – two case reports

Coccidioidomycosis is an endemic fungal infection in the southwestern United States, Mexico, and some areas of Central and South America [1]. It was first described by an Argentinean medical student, Alejandro Posadas, in 1892 [2]. Infection occurs following the inhalation of Coccidioides immitis (endemic to California) or posadasii (endemic to other regions mentioned above) spores. It has an estimated incidence of over 100,000 cases annually in the U.S. with most of these infections (one-half to two-thirds) manifesting subclinically or with only mild, isolated respiratory complaints [3‐6]. Rare cases (1 ~ 5%) may cause extrapulmonary or disseminated disease [1, 5, 7, 8]. Skin, lymph node, musculoskeletal, and central nervous system have been described as sites of dissemination [1, 7, 9]. We present two cases of coccidiomycosis mimicking a primary neoplasm of the patella in healthy, immunocompetent males. While coccidioidomycosis is known to involve the skeleton, we are unaware of a case that has presented as a primary lesion of the patella mimicking a neoplasm.

Individuals at risk for Coccidiomycosis dissemination include persons of Filipino or African ancestry, pregnant or postpartum women, and immunocompromised patients [3‐5, 10, 11]. Musculoskeletal infection by fungal infections, including Coccidioides spp., was once rare [1]. The incidence is increasing, not only in immunocompromised patients but also among healthy persons [1]. In some series it even accounts for 20% to 50% of disseminated cases [7]. The knee and the spine are the most commonly affected musculoskeletal sites [7‐9, 12]. Often, fungal arthritis follows a chronic indolent course of several months that may lead to delays in diagnosis and inappropriate treatments [1]. Skeletal manifestations associated with coccidioidomycosis include a chronic granulomatous process in bones, joints, and periarticular structures [1, 13]. Coccidioidal arthritis should always be suspected when a patient has progressive arthritis and a history of travel to an endemic zone. Recent literature suggests that the majority of septic arthritis cases are bone coccidioidomycosis with secondary involvement of the joint [14]. A history of pulmonary disease or an abnormal chest radiograph helps confirm the diagnosis [1].

To formally establish a diagnosis of coccydiomycosis, Maves et al. proposed serologic testing, histopathologic confirmation, or growth of Coccidioides in culture [5]. A positive mycological culture may grow relatively rapidly after inoculation into media (e.g. 48 hours), although 5 days or longer is required to be negative [3, 15]. Serologic testing plays an important role in the non-invasive diagnosis of patients with coccidioidomycosis [3, 5, 9, 10]. The IgM antibodies appear in the acute stage, and can detect in up to 75% of primary cases. With chronic infection, IgG antibodies are found and persist in relation to the extent of disease. The sensitivity of the IgG antibody test by Szeyko et al. in 36 chronic vertebral involvement cases, yielded a sensitivity of 88%. However, sensitivity of the test was lower in immunocompromised group than for immunocompetent patients (67% vs 93%) [9]. Inflammatory markers as ESR and CRP may also suggest the diagnosis of infection, but no clear relationship to the ratios has been noted [9].

Imaging findings in musculoskeletal coccidioidocomycosis are nonspecific [8]. The most frequent radiographic findings are that of multiple lytic, punched-out lesions. Lesions with permeative or moth-eaten borders, or sclerotic margins may be identified depending on chronicity and aggressivity of infection [12]. MRI and bone scan are nonspecific [8, 13]. The most common finding by MRI is hypertrophied synovium [8]. Other findings may include bone marrow edema or subchondral bone loss [8]. Distinguishing coccidioidal from tuberculous synovitis by imaging is not possible [11]. It is important to firmly establish the diagnosis before initiating what may be inappropriate treatment thereby delaying appropriate management. Despite many non-invasive techniques, synovial biopsy and culture still remains the most effective way to determine the true diagnosis [11].

Though our first patient presented with a prior history of coccidioidomycosis, failure of the culture result and previous occult lab findings were obfuscating. Our second patient had no antecedent history of fungal infection; however, he did live in an endemic area. In both cases, the presence of an isolated osteolytic lesion made the distinction between infection and tumor more challenging.

We are aware of two case reports describing chronic coccidiodomycosis of the knee [15, 16]. In these cases the disease involved the synovium and cancellous bones of distal femur and proximal tibia, which were treated with joint debridement, synovectomy, and antifungal drugs. To our knowledge, these are the first reported cases of patellar involvement in an immunocompetent adult. We suggest that orthopaedic surgeons and radiologists keep in mind that the chronic fungal infections such as this can mimic a bone or soft tissue neoplasm.