Which disorder is most accurately diagnosed when a patient presents with impaired single-word retrieval but has preserved single-word comprehension?

In this scenario, the most accurate diagnosis is anomic aphasia. Anomic aphasia is characterized primarily by difficulties in retrieving words or names while individuals maintain intact comprehension of single words. Patients often know what they want to say but struggle to find the correct word, reflecting a focus on the expressive component of language.

This clear distinction in anomic aphasia—between impaired word retrieval and preserved comprehension—makes it the most fitting choice in this context. Individuals with this condition frequently exhibit preserved ability to understand spoken and written language, which aligns with the symptoms described.

Other types of aphasia mentioned would not align as closely with the symptomatology presented. For example, Broca's aphasia typically involves both expressive and receptive language difficulties, leading to impaired comprehension alongside expressive challenges. Primary progressive aphasia encompasses various syndromes that generally involve more than just a word retrieval issue, including progressive deterioration in language abilities. Transcortical motor aphasia shares some similarities with Broca's aphasia but is less focused on single-word retrieval and can involve more severe comprehension deficits.

Thus, the specificity of impaired single-word retrieval alongside preserved comprehension distinctly points to anomic aphasia as the correct and most accurate diagnosis.