Isolated sesamoid lesions are rare, with few isolated case reports in the literature. Benign and malignant lesions appear most often in the metatarsals, with the calcaneus being the second most commonly afflicted site.9 The typical differential diagnosis for isolated lytic bone lesions includes fibrous dysplasia, osteoblastoma, giant cell tumor, metastatic lesion, multiple myeloma, aneurysmal bone cyst, chondroblastoma, brown tumor, infection, eosinophilic granuloma, enchondroma, and bone cyst, with no reports in the literature to our knowledge of these entities presenting in the hallux MTPJ sesamoid. In contrast, gout typically begins with normal radiographic findings, and later leads to erosive, “punched out” lesions on either side of the MTPJ.2
Hyperuricemia is an essential part of the pathophysiology of gout, but not all patients with an acute gouty attack have elevated uric acid levels and, in contrast, may actually have normal or low levels in 12% to 43% of cases.8 The most accurate time frame for assessment of serum uric acid levels is 2 weeks or more after subsidence of an acute event.8 The normal uric acid levels seen in our patient were most likely due to the fact that the workup was undertaken during an acute attack. The difficulty with establishing the diagnosis was compounded by bilateral involvement, history of trauma, negative joint aspiration, and atypical radiographic findings. A number of reports have described patients with tophus deposits prior to or in the absence of gouty arthritis or a gouty attack.10 Risk factors for this presentation include female sex, the predominant or exclusive involvement of fingers, chronic kidney disease, and treatment with a diuretic or anti-inflammatory drug.10
Conclusion
Our case report illustrates the difficulty in diagnosing an acute gouty attack in a patient with a history of trauma and atypical radiographic findings. The hallux MTPJ is the most common location of acute gouty attacks, but the medial sesamoid as an isolated location is a rare site of presentation. The combination of pain isolated to palpation of the sesamoid and radiographs that showed an aggressive and rapidly expansile lesion of the medial sesamoid raised concerns about a neoplastic lesion. Practitioners should consider acute gout in patients with sesamoid pain and with radiographs showing an expansile sesamoid lesion.