Which diagnostic study is best to evaluate possible underlying causes for persistent mood symptoms in a middle-aged man?

The best choice for evaluating possible underlying causes for persistent mood symptoms in a middle-aged man is thyroid tests. Mood disorders can have a variety of biological and physiological contributors, and thyroid function has a well-established relationship with mood regulation. Abnormal thyroid hormone levels, such as hypothyroidism or hyperthyroidism, can lead to symptoms that mimic or exacerbate mood disorders like depression or anxiety.

In middle-aged individuals, changes in thyroid function can occur and may sometimes be overlooked as a potential contributor to mood symptoms. Therefore, assessing thyroid function through tests can help determine if there is an organic cause that needs to be addressed, potentially improving the patient's mood symptoms when treated.

Other diagnostic options, such as cognitive testing, brain MRI, and neuropsychological evaluation, while useful in different contexts, do not specifically target the potential underlying organic causes associated with mood symptoms. Cognitive testing is primarily focused on assessing cognitive function rather than identifying mood disorders or their biochemical underpinnings. A brain MRI might be beneficial in certain cases, especially if there are neurological symptoms or concerns about structural brain issues, but it is not the first approach for mood symptoms. Similarly, a neuropsychological evaluation is more focused on assessing cognitive abilities and psychological issues rather than directly identifying medical contributors to mood