Adult onset confusional migraines have been documented.
HEALTH There are three primary classifications of migraines and headaches with several subcategories. Migraines are not always preceded by an aura. Some migraines may not include headache. Acute confusional migraine (ACM) is considered a rare migraine variant primarily seen in children and adolescents. ACM often arises after minor head injury and results in short-lived episodes of amnesia, inability to concentrate, disorientation, agitation, exhaustion and speech impairment. [1-4]
ACM episodic symptoms can linger for 6 to 24 hours with similarities to vertiginous migraines. Historically, ACM has been considered for adolescents whereas vertiginous or some other migraine variant suspected for adults. A clinical study by Andreas R. Gantenbein, MD, et al. in Switzerland documents 10 cases involving migraine sufferers aged 16 to 62. Patients did not manifest every symptom of ACM. In all patients, disorientation, memory problems, difficulty in recognizing familiar people and speech disturbance lasting several hours were frequently observed. Amnesia was not a major symptom. The frequent association with mild head trauma as a trigger was less consistent. 
The authors suggest that ACM might be the most appropriate term for a transient benign disorder that is likely to be a complex aura phenomenon, whereas “migraine encephalopathy” might be preferred in the context of trauma or in association with alterations of consciousness and/or abnormalities in imaging or other investigations. They further suggest expanding the concept of confusional migraine beyond the pediatric population to adults.
Another report suggests intravenous valproic acid may be able to quickly resolve sudden onset acute confusional migraine.  Sleep may also represent a useful laboratory feature in the diagnosis of ACM.  This information may be helpful to neurologists treating adults presenting symptoms of confusional migraines.
- International Headache Society (IHS). ihs-classification.org
- What Is a Silent Migraine?. webmd.com
- Migraine variants and beyond. Srinivasa R, Kumar R. ncbi.nlm.nih.gov
- What are acute confusional migraines? healthguru.com
- Confusional migraine is an adult as well as a childhood disease. (PDF) Gantenbein A R, et al. zora.uzh.ch
- Valproic Acid Resolves Girl's Acute Confusional Migraine. modernmedicine.com
- Acute confusional migraine attacks resolved by sleep. Parrino L, et al. onlinelibrary.wiley.com