A case of an arachnoid cyst masquerading as corticobasal degeneration.

We present an individual, "JD", a 69-year-old Caucasian, married female with symptoms that included progressive right arm stiffness, tremor, and clumsiness; increasing gait and balance disturbance; increased fatigue and emotionality. Neuropsychological evaluation revealed compromised semantics and language-associated functions; impaired visual constructional ability; markedly reduced cognitive and visuomotor processing speed; low average to average working memory; variable praxis performance; variable abstract reasoning, problem solving, and set shifting; and lower overall intellectual functioning compared to premorbid estimates. Overall, her neuropsychological profile indicated marked compromise of the frontal and left parietal regions. The data coupled with her symptom pattern and demographics partially fit corticobasal degeneration diagnostic criteria. Neuroimaging, however, performed 2 years prior to the assessment and again during the current workup revealed an enlarging arachnoid cyst compressing the left parietal and posterior frontal lobe and a small portion of the right medial frontal-parietal region. We discuss the neuroanatomical substrates involved in her cognitive presentation and how two very distinct pathological processes (corticobasal degeneration, arachnoid cyst) can result in two similar symptom presentations. We summarize how multidisciplinary assessment assists with differential diagnosis and treatment planning.