Earache, headache, blurred vision - ear issue or neurological?
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This may not fit due to the sudden onset of your son's symptoms, but you may want to investigate the possibility of TMJ. I suffered from strange daily headaches for nearly a year before being diagnosed and treated for TMJ. Given the close relationship between the jaw and ear and your son's symptoms with opening his mouth, it may be worth investgating. The other thing that comes to mind when I read your posting are migraine headaches, mainly due to the blurry vision. They are rare but not unheard of in boys. Finally, since the symptoms seem more acute than chronic I would think that a CT scan or MRI to rule out anything structural would be wise. How old is your son?
Best wishes!
ALL persistent headaches need to be investigated promptly in a child. The change in vision is also concerning. Certainly the closeness in time to an ear infection and the onset of headache with opening the mouth widely (changing the pressure in the middle ear) suggest a problem in the ear, but never in pediatrics do you ignore a persistent symptom like a headache just because it is "likely" something common and benign. I (as a retired pediatrician) encourage you to firmly request a CT scan, and if this is normal I agree with the poster above about an ENT exam, but would add an pediatric ophthamologist (eye specialist). If your child's doctor won't do it, look for one that takes you seriously.
I was very conservative in Pediatrics and, looking back now, do not regret my policy of looking harder for the serious problems that sneak up among the routine. It's sure beats looking back on missed diagnoses because I was too cavalier. It's always a thin line between raising too much concern (though I found that parents are actually relieved by the act of taking their concerns seriously) and knowing that "most" things are not serious.
I hope this made sense. I've taken my evening meds and am sleepy.
Good luck, Quix