Which of the following symptoms is used to diagnose a migraine headache?

The symptom of pulsatile or throbbing pain, nausea, and unilateral location is a key indicator for diagnosing migraines. Migraines are characterized by specific features that differentiate them from other types of headaches. The throbbing or pulsing quality of the pain is particularly notable during a migraine attack, making it distinct from other headache types, which may present as more steady or pressing.

Additionally, nausea is commonly associated with migraines, often accompanied by vomiting or sensitivity to light and sound, further supporting the diagnosis. The unilateral nature of the pain means it typically affects one side of the head, which is a classic symptom of migraines. The combination of these symptoms aligns closely with established diagnostic criteria for migraines, thereby solidifying option B as the correct choice.

Other options do not fit the classic migraine profile; for example, vision changes with aura may occur in some migraine cases but are not definitive for diagnosis, while continuous dull headaches are often seen in tension-type headaches. Allergy symptoms do not correlate with migraines, which points to the specificity of the symptoms listed in option B.