Background Clinical assessments and uniplanar images in temporomandibular disorders are not always entirely reliable. This predicament is especially important when clinicians need to determine the nature of temporomandibular joint disease, particularly when clinical features are not helpful in determining the diagnosis. Clinical presentation A 63-year-old female patient presented with mild pain in her right TMJ. During routine imaging exams, a destructive monoarticular arthritis was noticed, producing multiple erosions of the mandibular and temporal condyles. In addition, attrition of the ceiling of the glenoid fossa was observed, generating a communication with the endocranium. Only the presumptive biological behavior revealed on TMJ imaging and the appearance of the psoriatic plaques later during follow-up helped the authors to narrow the differential diagnosis. Conclusion The clinical case presented illustrates the difficulties in diagnosing an erosive, seronegative TMJ destruction, suggestive of a systemic arthritis.