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What is Chronic paroxysmal hemicrania and explain in detail?
Chronic paroxysmal hemicrania (CPH) is a severe debilitating unilateral headache usually affecting the area around the eye.  It normally consists of multiple severe, yet short, headache attacks affecting only one side of the cranium. It is more commonly diagnosed in women than in men, but, unlike a migraine, has no neurological symptoms associated with it. CPH headaches are treated through the use of non-steroidal anti-inflammatory drugs, with indomethacin found to be usually effective in eliminating symptoms.
Paroxysmal hemicrania is classified by the frequency and duration of attacks experienced by patients.  Episodic paroxysmal hemicrania attacks occur at least twice a year and last anywhere from seven days to a year with pain free periods of a month or longer separating them. Chronic paroxysmal hemicrania attacks occur over the course of more than a year without remission or with remissions lasting less than a month.

Signs and symptoms
Individuals with CPH suffer multiple short, severe headaches a day, often more than five, with most lasting between 5 and 30 minutes each. When compared to cluster headaches, CPH attacks are typically shorter. Each headache is centered around the eye, temple and forehead and is localized to one side of the head. While redness and watering of the eye are associated with CPH, patients typically do not experience nausea or vomiting. Although less common, CPH may also present as severe unilateral ear pain accompanied by autonomic symptoms. Autonomic symptoms may include the presence of Red Ear Syndrome.Attacks hit the patient many times a day, from 5 times a day up to 40 times a day with an average of 11 a day. Mild background pain can persist between attacks. They come in bouts that last from 7 days to 1 year separated by remission periods that can last more than 3 months in episodic patients, or less than 3 months in chronic patients. Onset is in adulthood and the disorder may last indefinitely or spontaneously go into remission. Circadian mechanisms are likely involved in paroxysmal hemicrania due to its highly cyclic nature. No particular circannual recurrence characterizes symptomatic periods, although some patients can experience a seasonal preponderance.

Causes
The causes of paroxysmal hemicrania are ultimately still unknown. Sympathetic symptoms such as miosis and ptosis might be linked with a generalized sympathetic dysfunction. Neuropathic mechanisms may be involved, since attacks can be triggered by mechanical stimulation. Perivascular neurogenic inflammatory processes can worsen symptoms or increase pain. Dilated blood vessels may contribute in stimulating trigeminal nociceptors directly, although they cannot be the origin of pain, since even suppression of vasodilation does not stop it once it’s started.Many secondary conditions have been reported to be possible causes of CPH, according to Mehta et al., most of which are arterial abrasions or tumors. These include aneurysms in the circle of Willis, middle cerebral artery infarction, parietal arteriovenous malformation, cavernous sinus and petrous ridge meningiomas, pituitary adenoma, Pancoast tumor, gangliocytoma of the sella turcica, and malignant frontal tumors. This accentuates the urgency for those diagnosed with CPH to receive an MRI head scan.

Diagnosis
CPH is a long-term disease with symptoms lasting for longer than a year, either without remission or with remissions that last less than a month. In order to be diagnosed with CPH, a patient needs to have had at least 20 attacks filling the following criteria:
Attacks of severe unilateral orbital, supraorbital, or temporal pain lasting between 2 and 30 minutes.
The headache needs to take place with one of the following:
Ipsilateral conjunctival injection and/or lacrimation
Ipsilateral nasal congestion and/or rhinorrhoea
Ipsilateral eyelid oedema
Ipsilateral forehead and facial sweating
Ipsilateral miosis and/or ptosis
Attacks need to occur more than five times a day for more than half of the time, although periods of lower frequency can occur.
The symptoms cannot be attributed to another disorder.
Attacks can be prevented completely by therapeutic doses of indomethacin.In addition, diagnosis of CPH requires that neuropathy of the supraorbital area in the temporal branch of the facial nerve be ruled out.

Comparison to cluster headaches
Though outwardly similar to cluster headaches, chronic paroxysmal hemicrania is rather different, and the two headaches are not a subset of one or the other