Hemicrania continua
Hemicrania continua (HC) is a persistent unilateral headache that responds to indomethacin. It is usually unremitting, but rare cases of remission have been documented. Hemicrania continua is considered a primary headache disorder, meaning that it's not caused by another condition.

# Diagnostic criteria
International Headache Society's International Classification of Headache Disorders 2nd Edition, establishes the following diagnostic criteria for hemicrania continua:
- Headache for more than 3 months fulfilling other 3 criteria:
- All of the following characteristics:
Unilateral pain without side-shift
Daily and continuous, without pain-free periods
Moderate intensity, but with exacerbations of severe pain
- Unilateral pain without side-shift
- Daily and continuous, without pain-free periods
- Moderate intensity, but with exacerbations of severe pain
- At least one of the following autonomic features occurs during exacerbations and ipsilateral to the side of pain:
Conjunctival injection and/or lacrimation
Nasal congestion and/or rhinorrhea
Ptosis and/or miosis
- Conjunctival injection and/or lacrimation
- Nasal congestion and/or rhinorrhea
- Ptosis and/or miosis
- Complete response to therapeutic doses of indomethacin
A variant on hemicrania continua has also been described, in which the attacks may shift sides, although meeting the above criteria in all other respects.

# Epidemiology
Hemicrania continua was first described in 1981, at that time around 130 cases were described in the literature.  However, rising awareness of the condition has led to increasingly frequent diagnosis in headache clinics, and it seems that it is not as rare as these figures would imply. The condition occurs more often in women than men and tends to first present in adulthood, although it has also been reported in children as young as 5 years old.

# Cause and diagnosis
The cause of hemicrania continua is unknown. There is no definitive diagnostic test for hemicrania continua. Diagnostic tests such as imaging studies may be ordered to rule out other causes for the headache. When the symptoms of hemicrania continua are present, it's considered "diagnostic" if they respond completely to indomethacin.
The factor that allows hemicrania continua and its exacerbations to be differentiated from migraine and cluster headache is that hemicrania continua is completely responsive to idomethacin. Triptans and other abortive medications do not affect hemicrania continua.

# Symptoms
In addition to persistent daily headache of HC, which is usually mild to moderate, HC can present other symptoms. These additional symptoms of HC can be divided into three main categories:
- Autonomic symptoms:
conjunctival injection
tearing
rhinorrhea
nasal stuffiness
eyelid edema
forehead sweating
- conjunctival injection
- tearing
- rhinorrhea
- nasal stuffiness
- eyelid edema
- forehead sweating
- Stabbing headaches:
Short, "jabbing" headaches superimposed over the persistent daily headache.
Usually lasting less than one minute.
- Short, "jabbing" headaches superimposed over the persistent daily headache.
- Usually lasting less than one minute.
- Migrainous features:
throbbing pain
nausea and/or vomiting
phonophobia
photophobia
- throbbing pain
- nausea and/or vomiting
- phonophobia
- photophobia

# Differential Diagnosis of Hemicrania continua

# Treatment
Hemicrania continua generally responds only to indomethacin 25-300 mg daily, which must be continued long term. Unfortunately, gastrointestinal side effects are a common problem with indomethacin, which may require additional acid-suppression therapy to control.
In patients who are unable to tolerate indomethacin, the use of celecoxib 400-800 mg per day (Celebrex) and rofecoxib 50 mg per day (Vioxx - no longer available) have both been shown to be effective and are likely to be associated with fewer GI side effects. There have also been reports of two patients who were successfully managed with topiramate 100-200 mg per day (Topamax) although side effects with this treatment can also prove problematic.