Fahr’s disease and Aicardi–Goutières syndrome (AGS) are rare neurogenetic disorders that share radiologic hallmarks of basal ganglia calcifications but diverge in etiology. Fahr’s disease represents a primary familial brain calcification associated with progressive neuropsychiatric and motor decline without systemic inflammation. AGS, conversely, is a type I interferonopathy caused by mutations in nucleic acid metabolism genes (TREX1, RNASEH2A/B/C, SAMHD1, ADAR1, and IFIH1), producing chronic neuroinflammation, leukoencephalopathy, and variable movement disorders. While dystonia and chorea are documented in AGS, palatal myoclonus has not previously been reported.

We present a 51-year-old male presented with left foot drop and was found on electromyography to have a sensory neuronopathy/large-fiber polyneuropathy. He developed a progressive steppage gait and involuntary lower-extremity movements/tremors which prompted evaluation by a movement disorder specialist. Neurological examination revealed palatal myoclonus and left leg dystonia, and his Brain CT demonstrated basal ganglia calcifications, initially suggesting Fahr’s disease. However, the coexistence of palatal myoclonus, a finding typically indicative of brainstem or dentato–olivary pathway dysfunction, was not typical of Fahr’s disease. The varying symptoms opened the possibilities of rarer diseases and thus he was recommended to undergo Genetic testing which subsequently confirmed a pathogenic variant consistent with Aicardi–Goutières syndrome, establishing a novel adult-onset phenotype.

Fahr’s disease classically manifests as symmetric basal ganglia calcifications with parkinsonism or cognitive decline in the absence of inflammatory or immune features. In contrast, this patient’s presentation, marked by palatal myoclonus and dystonia, signaled involvement beyond the basal ganglia, suggesting inflammatory or brainstem pathology inconsistent with Fahr’s disease. This prompted genetic testing that revealed AGS. The case emphasizes the continued diagnostic value of the neurologic examination and maintaining a broad differential when imaging and clinical findings diverge. Moreover, it introduces palatal myoclonus as a novel manifestation of AGS, expanding the recognized motor spectrum of this interferonopathy.