Hemicrania continua (HC)

Hemicrania continua (HC) is a chronic and persistent unilateral headache and considered as one of primary headache disorders, according to International Headache Society's International Classification(1), affecting 4 to 5% of the general population.

I. Symptoms
In the report of two patients with side-shifting HC with aura, showed that these patients' symptoms are [1]unilateral headaches, [2]visual aura, [3]autonomic features, [4]throbbing pain, [5]nausea and [6]photo/phonophobia(2), runny nose[7], tearing and redness of the eyes[8], sweating[9], drooping eyelids[10] nausea, vomiting[11] and sensitivity to light[12](3). Other symptoms include trigeminal-autonomic cephalalgias[13] and migraine[14] (4)

II. Causes and Risk factors
Some researchers suggested that that secondary or symptomatic HC is associated with another neurological or non-neurological disease. In the a report of three patients with secondary HC and the also review the literature to identify the clinical predictors of an underlying disease entity. Intracranial structural lesion, head and neck vessel pathology, and carcinoma lung should be suspected in every patient. The factors that may suggest a secondary pathology are: elderly age, male sex, smoking habit, constitutional symptoms, symptoms related to respiratory system, frequent and short-lived exacerbation, nocturnal exacerbation, HC evolving from remitting form, recent neck and/or head trauma, miosis, elevated ESR, and fading effect of indomethacin. We recommend MRI brain in all the patients presenting with HC or HC like headache. Angiography and CT chest are two other investigations that may be supplemented in patients with high risk for head/neck vessel pathology and carcinoma lung.(5).
Other researchers suggested that patient who suffered from cluster headache may evolving into ipsilateral HC, as they do not tolerate a long-term indomethacin therapy(6). Other found that HC is a life long condition, and skipping of a single dose of indomethacin usually leads to reappearance of headache(7)

Misdiagnosis 
Diagnosis is difficult, in a report of a woman in her fifties, with a long history of side-locked unilateral headache, was hospitalized for left-sided side-locked paroxysmal headache (attacks with 10-20 min duration), indicated that a retrospective review of her medical history showed 15 years of unsuccessfully treated unilateral headache, until she responded completely to rofecoxib. Ipsilateral cranial autonomic symptoms also supported the diagnosis of hemicrania continua, although these symptoms presented before indomethacin was tried. Diagnostic delay and misdiagnoses of unilateral headaches, as illustrated by this case, shows the clinical controversies and difficulties in diagnosing and treating this condition.(8).
Others suggested that Misdiagnosis of HC is probably common in general neurology settings and other clinical specialties. Dr. Peres MF and the team at the UNIFESP (Universidade Federal de São Paulo), São Paulo, said "the gap between the correct and misdiagnosis of this disorder. HC was once thought to be a rare headache disorder, but is, in fact, an under-recognized headache syndrome. HC can be of continuous or remitting form. Variants such as HC with aura have been described and secondary cases may occur"(9)

Diagnosis 
many researchers believe the diagnosis of Hemicrania continua (HC) consists of the symptoms and signs of  [1]unilaterality without side shift; [2]absolute indomethacin effect; [3] and long-lasting repetitive attacks of varying duration[4], eventually with a chronic pattern, the pain being mild to severe[5](10).Other suggested clinically, HC is considered a syndrome with two pivotal characteristics: (i) strictly unilateral (moderate, fluctuating, relatively long-lasting) headache; and (ii) absolute response to indomethacin. HC is further characterized by some ancillary, but mostly "negative", features such as: (iii) relative paucity of accompaniments; and (iv) lack of precipitating factors.(11)

Treatments
1. Indomethacin
Many researchers believe that Hemicrania continua is one of the indomethacin-responsive headache syndromes, patients may require daily indomethacin for years. The risks of long-term indomethacin include gastrointestinal and renal dysfunction, but according to the study from the team and Dr. JA Pareja found that Six (23%) patients showed adverse events, mostly gastrointestinal and relieved with ranitidine. No major side-effects were observed. These results indicate that prolonged indomethacin treatment of HC or CPH has a good safety and tolerability profile with a reduction of up to 60% in the initial dose.

2.  Melatonin
Other suggested that Melatonin is a pineal hormone with a chemical structure very similar to indomethacin as melatonin was shown to be effective for primary stabbing headache, another indomethacin-responsive syndrome.(12)

3.  Other studies point out possible alternatives: Gabapentin, topiramate, cyclooxygenase-2 inhibitors, piroxicam, beta-cyclodextrin, amitriptyline, melatonin. Other drugs were described in different reports as efficient, but most of them were considered inefficient in other HC cases.(13) and a report of two cases of HC responsive to topiramate and review the available alternatives for the patients of HC. The side effects of indomethacin in the various headache disorders and other painful conditions, and may need for trial of other drugs for the patients of HC.(14)

4. Etc.

Side effects
Side effects of indomethacin are not limit to
1. Indomethacin HC is a life long condition, and
2. Skipping of a single dose of indomethacin usually leads to reappearance of headache.(14)
3. risk for serious stomach/intestinal bleeding.
4. Others not common side effects include chest pain, shortness of breath, weakness on one side of the body, sudden vision changes, slurred speech.
5. Gastrointestinal and renal dysfunction.(15)
6. Etc.

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Sources
(1) http://www.ihs-headache.org/upload/ct_clas/ihc_II_main_no_print.pdf
(2) http://www.ncbi.nlm.nih.gov/pubmed/16886926
(3) http://headaches.about.com/lw/Health-Medicine/Conditions-and-diseases/All-About-Hemicrania-Continua-Headaches.htm
(4) http://www.ncbi.nlm.nih.gov/pubmed/22440373
(5) http://www.ncbi.nlm.nih.gov/pubmed/19215945
(6) http://www.ncbi.nlm.nih.gov/pubmed/19006550
(7) http://www.ncbi.nlm.nih.gov/pubmed/19041987
(8) http://www.ncbi.nlm.nih.gov/pubmed/21494306
(9) http://www.ncbi.nlm.nih.gov/pubmed/19769451
(10) http://www.ncbi.nlm.nih.gov/pubmed/11903280
(11) http://www.ncbi.nlm.nih.gov/pubmed/11843864
(12) http://www.ncbi.nlm.nih.gov/pubmed/16866728 
(13) http://www.ncbi.nlm.nih.gov/pubmed/22440373
(14) http://www.ncbi.nlm.nih.gov/pubmed/19041987
(15) http://www.ncbi.nlm.nih.gov/pubmed/16866728