N. B. Migraine Headaches and Chronic Migraine are different conditions.  Botolinum Toxin Injections are indicated as treatment only for chronic migraine. 

1. Migraine Headaches

A migraine is a type of headache. It may occur with symptoms such as nausea, vomiting, or sensitivity to light and sound. In many people, a throbbing pain is felt only on one side of the head.

CAUSES

A migraine headache is caused by abnormal brain activity. This activity can be triggered by many things. But the exact chain of events remains unclear. Most medical experts believe the attack begins in the brain and involves nerve pathways and chemicals. The changes affect blood flow in the brain and surrounding tissues.

Migraine headaches tend to first appear between the ages of 10 and 45. Sometimes, they begin earlier or later. Migraines may run in families. Migraines occur more often in women than men. Some women, but not all, have fewer migraines when they are pregnant.

Migraine attacks may be triggered by any of the following:

• Caffeine withdrawal
• Changes in hormone levels during a woman’s menstrual cycle or with the use of birth control pills
• Changes in sleep patterns, such as not getting enough sleep
• Drinking alcohol
• Exercise or other physical stress
• Loud noises or bright lights
• Missed meals
• Odors or perfumes
• Smoking or exposure to smoke
• Stress and anxiety

Migraines can also be triggered by certain foods. Most common are:

• Chocolate
• Dairy foods, especially certain cheeses
• Foods with monosodium glutamate (MSG)
• Foods with tyramine, which includes red wine, aged cheese, smoked fish, chicken livers, figs, and certain beans
• Fruits (avocado, banana, citrus fruit)
• Meats containing nitrates (bacon, hot dogs, salami, cured meats)
• Onions
• Peanuts and other nuts and seeds
• Processed, fermented, pickled, or marinated foods

True migraine headaches are not a result of a brain tumor or other serious medical problem. Only a health care provider who specializes in headaches can determine if your symptoms are due to a migraine or other condition.

Source 

2. Chronic Migraine

Migraine is a common and disabling condition reported in approximately 12% of the population. In the Global Burden of Disease Study by the World Health Organization, updated in 2013, migraine was found to be the sixth highest cause worldwide of years lost due to disability. Migraine attacks sometimes increase in frequency over time. Headache experts divide this process of transition into four distinct states:

• No migraine
• Low-frequency episodic migraine (less than 10 headache days per month)
• High-frequency episodic migraine (10-14 headache days per month)
• Chronic migraine (15 or more headache days per month; meaning that people with chronic migraine have a migraine or headache more often than not)

As per the International Headache Society, chronic migraine is defined as headache occurring on 15 or more days per month for more than three months, which, on at least 8 days per month, has the features of migraine headache. Chronic migraine occurs in approximately 1% of the population. Studies estimate that about 2.5% of people with episodic migraine will transition to chronic migraine each year.

To make a diagnosis of chronic migraine, it is very important to know the exact number of days per month that a person experiences a headache of any kind. This is best done my maintaining a daily headache diary. Often when people are asked how many headaches they have, they may report only their most severe headaches (like the ones that keep them from work/school or the ones that they take medications for). By reporting only their most severe headaches, they may give the doctor a false impression of their true headache burden and consequently a diagnosis of chronic migraine may be missed.

People suspected of having chronic migraine should be carefully assessed by their doctor to exclude other potential causes of frequent headaches such as secondary headaches (meaning headaches caused by an underlying condition or disease) or other forms of chronic daily headache including chronic tension-type headache, hemicrania continua, or new daily persistent headache.

Risk Factors for Chronic Migraine

Transition to chronic migraine is associated with well-recognized, potentially treatable risk factors. Some examples of risk factors include:

• Depression
• Anxiety
• Other pain disorders
• Obesity
• Asthma
• Snoring
• Stressful life events
• Head/Neck injury
• Caffeine
• Acute medication overuse
• Persistent, frequent nausea

Treatment

Treatment of chronic migraine is similar to that of episodic migraine with a few notable exceptions. Treatment should consist of:

• Acute medications for use at onset of a headache attack to try to break it. Limitation on number of uses of acute medications is important to try to avoid medication overuse and risk of medication overuse headache
• Preventive medications to help reduce the frequency and severity of headache attacks.
• Onabotulinumtoxin A (Botox) is an FDA approved preventive treatment for chronic migraine.
• Preventive treatments used for episodic migraine such as anti-seizure medications (Example: depakote, topiramate), anti-depressants (Example: amitriptyline, venlafaxine) and blood pressure medications (Example: propranolol) may also be used for chronic migraine prevention.
• Non-medication preventive treatments including biofeedback, cognitive behavioral therapy
• Addressing risk factors such as depression, anxiety, snoring, obesity, etc.
• Botulinum Toxins are not a cure and combined with additional treatment(s) to maintain the benefit

Resources:

https://americanmigrainefoundation.org/resource-library/chronic-migraine/

https://www.ubrelvy.com/

https://www.nurtec.com/

https://headaches.org/2007/11/19/facts-about-triptans/