These additional symptoms of HC can be divided into three main categories:

Autonomic symptoms:
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. Migrainous features:
throbbing pain
nausea and/or vomiting
phonophobia
photophobia

Cause
The cause of hemicrania continua is unknown. Diagnosis
The following diagnostic criteria are given 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
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
Complete response to therapeutic doses of indomethacin, although cases of hemicrania continua that do not resolve with indomethacin treatment have been documented.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.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, its considered "diagnostic" if they respond completely to indomethacin. The efficacy of indomethacin may not be long term for all patients, as can eventually become ineffective. Differential diagnosis
The factor that allows hemicrania continua and its exacerbations to be differentiated from migraine and cluster headache is that hemicrania continua is characterized by complete response to therapeutic doses (25–300 mg) of indomethacin.
2, by G.S.Davis, and the incident has been cited in Kings American Dispensatory (1898 and later editions) in the description of the strong analgesic Jamaican Dogwood, a relatively low dose of which reportedly produced convulsions and prolonged respiratory depression over six hours in an elderly woman with this condition.In newer times, Hemicrania continua was 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 present first in adulthood, although it has also been reported in children as young as 5 years old. References


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