Presentation and course
All cases of chronic unilateral daily headaches should have a trial of indomethacin (25). Indomethacin-responsive headaches are diverse in character and can be traditionally divided based on their response to indomethacin. Absolute responsiveness to indomethacin, defined as complete resolution of symptoms, is observed with paroxysmal hemicrania and hemicrania continua, whereas relative responsiveness is apparent in primary cough (Valsalva maneuver) headache, primary exercise headache, primary headache associated with sexual activity, and primary stabbing headache (13; 16).
Absolute responsiveness to indomethacin
Paroxysmal hemicrania. Paroxysmal hemicrania is a rare primary headache disorder belonging to the group of trigeminal autonomic cephalalgias (11). It is characterized by sudden bursts of severe, strictly unilateral head pain lasting 2 to 30 minutes, several times a day, in association with at least one ipsilateral cranial autonomic feature, such as conjunctival injection, lacrimation, nasal congestion, rhinorrhea, forehead and facial sweating, miosis, ptosis, eyelid edema, or a sense of restlessness or agitation (13). The attacks demonstrate an absolute response to indomethacin (13). Paroxysmal hemicrania can be classified as episodic or chronic, with the latter comprising 65% of patients (35). Episodic paroxysmal hemicrania is defined as attacks of paroxysmal hemicrania occurring in periods lasting from 7 days to 1 year, separated by pain-free periods lasting at least 3 months, whereas chronic paroxysmal hemicrania is characterized by attacks occurring for more than 1 year without remission or with remission periods lasting less than 3 months (13).
Paroxysmal hemicrania usually occurs in adulthood, with numerous case series reporting years of onset in the late third decade (05; 26; 13). There is no clear evidence of female preponderance (M:F ratio approximately 1:1) or racial preference (15; 05). Attacks are typically spontaneous with an absence of circadian periodicity; however, mechanical triggers, such as bending or rotating the head, account for 10% of paroxysmal hemicrania attacks, and attacks can be triggered by NO donor glyceryl trinitrate (08). Approximately 20% of patients believe alcohol is a trigger for paroxysmal hemicrania attacks, a distinguishing difference from cluster headaches in which alcohol is a well-known potent trigger in the majority of cases (11; 35). Notably, cutaneous triggers, such as touching the face, are not associated with paroxysmal hemicrania (35). Similarly, menstruation does not appear to worsen attacks, and pregnancy does not appear to terminate attacks (11).
Attacks of paroxysmal hemicrania are recurrent throughout the day, with one case series reporting a mean of 11 daily attacks lasting 17 minutes on average (05). The pain traditionally involves the ophthalmic division of the trigeminal nerve, with a typical pain distribution of V1>C2>V2>V3 (11). In one case series (n = 31), patients reported maximal tenderness at orbital and temporal locations (77%), followed by retro-orbital (61%), frontal (55%), and occipital (42%), amongst other locations, with 65% of patients rating their attacks as 10 out of 10 on a verbal rating scale (05). Of the cranial autonomic features reported, lacrimation was the most common (87%), followed by conjunctival injection (68%), rhinorrhea (58%), nasal congestion (55%), ptosis (55%), eyelid edema (42%), and forehead and facial sweating (32%); the least common was miosis (10%). Agitation is common throughout attacks and can be observed in 80% of patients (35). Migrainous features lateralized to side of the head pain are frequently reported in patients with paroxysmal hemicrania, with the highest associations to motion sensitivity (52%), nausea (43%), photophobia (30%), phonophobia (17%), and vomiting (17%) (05; 26). Outside of the acute attacks, interictal pain has been reported in 47% of patients; this is often described as intermittent and milder, unlike hemicrania continua (26; 32).
Hemicrania continua. Hemicrania continua was reclassified as a trigeminal autonomic cephalalgia in ICHD-3 beta as a result of its shared clinical and pathophysiological features with other trigeminal autonomic cephalalgia syndromes, such as unilateral head pain, cranial autonomic symptoms, and indomethacin responsiveness (14). It is characterized by a persistent, strictly unilateral headache that varies in severity and is associated with ipsilateral conjunctival injection; lacrimation; nasal congestion; rhinorrhea; forehead and facial sweating; miosis; ptosis or eyelid edema; or restlessness or agitation (13). The headache displays an absolute response to indomethacin (13). Hemicrania continua can be classified as remitting or unremitting. Patients with the remitting subtype may experience relief of symptoms for at least 24 hours as opposed to patients with the unremitting subtype who suffer from continuous pain for at least 1 year, without remission periods of at least 24 hours (13).
Hemicrania continua has been reported in a range of ages (31 to 79 years) with a mean age of 51 years reported in a large case-series study (n = 39) (04). It is somewhat more likely to occur in females (M:F ratio approximately 1:2) and is likely underdiagnosed as a result of its rarity and difficulties distinguishing interparoxysmal pain from other trigeminal autonomic cephalalgias, paroxysmal hemicrania, and the interparoxysmal allodynia observed in cluster headache (11; 35). Some patients report alcohol as a mild trigger of hemicrania continua, but it cannot be triggered by cutaneous touch or nitroglycerin (35).
Patients typically describe a persistent, baseline pain that is often dull in quality and of moderate severity (mean score of 5.8, measured by a verbal rating scale), with superimposed exacerbations of more intense, sharp, or throbbing pain that recur throughout the day (mean score of 9, measured by a verbal rating scale) (04). The pain is often described as “excruciating” (71%) and most commonly affects the frontal and temporal regions of the head (04; 32). Exacerbations are daily in 50% of patients, with an average attack duration ranging from 30 minutes to 3 days (35). Cranial autonomic features may be present unilaterally or bilaterally in exacerbations, with lacrimation being the most common (73%), followed by nasal congestion (51%), conjunctival injection (46%), ptosis (40%), and flushing (40%), amongst others (04). Moreover, agitation and restlessness are frequently observed during exacerbations in 69% and 28% of patients, respectively. Underlying migrainous biology additionally occurs, with 70.6% of patients meeting the diagnosis of migraine in the exacerbation period. Individuals often experience nausea (43% to 53%), photophobia (30% to 79%), and motion sensitivity (69%) (25; 04; 27).
Atypical cases of hemicrania continua have been reported and challenge the diagnostic criteria set by the International Headache Society, eg, cases of hemicrania continua with no cranial autonomic features or bilateral hemicrania continua. Indomethacin-nonresponsive hemicrania continua has been reported and suggests a different disorder (32).
Relative responsiveness to indomethacin
Primary cough (Valsalva maneuver) headache. Primary cough headache manifests as a sudden-onset bilateral headache dominating the posterior region of the head and is brought on by coughing, straining, or other Valsalva maneuvers (excluding prolonged physical exercise) in the absence of any other intracranial disorder (13). The headache arises moments after the cough or other Valsalva-associated stimulus and reaches peak intensity almost immediately; it then subsides over several seconds to a few minutes (although some patients report symptoms up to 2 hours) (13). Pain is generally described as moderate to severe with a stabbing, sharp, or splitting quality, and a significant correlation is observed between the frequency of cough and the severity of headache (13; 22). Associated symptoms can be seen in 60% of patients and include vertigo, nausea, and sleep abnormalities (13). It predominantly affects patients over the age of 40 with a mean age of onset of 70 years (range 44–81) and has a clear male predominance (12). The diagnosis of primary cough headache is confirmed by normal neuroimaging studies. In approximately 50% of patients seeking help for primary cough headache, a structural lesion is found. This is usually (approximately 90%) a Chiari type I deformity and, in a few cases, space-occupying lesions in the posterior fossa/foramen magnum area, which cause at least intermittent local blocking of CSF circulation, constituting a diagnosis of secondary cough headache (12; 22). Response to indomethacin cannot be used to differentiate primary and secondary cough headache, and neuroimaging is required to differentiate between the subtypes (03).
Primary exercise headache. Primary exercise headache is precipitated during or after physical exercise in the absence of any other intracranial disorder; patients must have at least two episodes to fulfil the diagnostic criteria set by the International Headache Society (13). On first presentation, it is important to exclude subarachnoid hemorrhage, arterial dissection, and reversible cerebral vasoconstriction syndrome (13). Primary exercise headache can occur in both trained and untrained athletes and may be triggered by any form of strenuous activity, which is often described as enough to double the resting pulse for over 10 seconds (12). Patients typically describe multiple episodes of pulsating, aching, and throbbing head pain that occur at the peak of exercise and extend up to 48 hours in some cases (13). The typical age of onset is below 50 years, and it is four times more common in men (12). Approximately 50% of patients with primary exercise headache also have a personal history of migraine. Secondary exercise headache should be suspected for (1) a single episode; (2) females; (3) other neurologic symptoms, such as loss of consciousness; (4) people older than 40 to 50 years old; and (5) a duration over 24 hours.
Primary headache associated with sexual activity. Primary headache associated with sexual activity is characterized by at least two episodes of headache that increase in intensity with increasing sexual excitation or mount to explosive intensity just before or with orgasm in the absence of any other intracranial disorder (13). Head pain has a median duration of 30 minutes; however, it may last up to 72 hours, with the first 24 hours potentially being severe (13; 12). On first presentation, it is important to exclude subarachnoid hemorrhage, intra- and extracranial arterial dissection, and reversible cerebral vasoconstriction syndrome (18). Patients typically describe a bilateral, occipital, or holocephalic head pain that starts as a dull ache and worsens with increasing sexual excitement, reaching peak intensity at orgasm (12). It has a clear male predominance (around 4:1) and usually begins between 20 to 45 years of age. Some patients may have comorbidities of hypertension, migraine, or tension-type headache (17).
Primary stabbing headache. Primary stabbing headache is defined as head pain occurring spontaneously as a single stab or series of stabs that recur with irregular frequency and last for a few seconds in the absence of cranial autonomic symptoms and underlying organic disease of the cranial nerves (13). Stabs are sudden onset, with 80% of stabs lasting for 3 seconds or less, and they are most frequently reported in extratrigeminal locations in 70% to 80% of patients (13; 16). Stabs can be multifocal and migrate between areas; this has been observed in up to 64% of patients (16). Relative indomethacin responsiveness has been described, with a success rate of complete remission of between 30% to 50%.
Clinical vignette
Case 1. Hemicrania continua. A 47-year-old female presented with a 7-year history of daily right-sided headache. She described a constant, generalized headache of mild intensity that waxed and waned in severity, but never completely resolved. Her husband said that her right eye watered and her eyelid looked droopy when the pain was bad. She had no other medical conditions. She had a normal neurologic examination. Routine laboratory studies and neuroimaging (MRI head) were normal.
Case 2. Episodic paroxysmal hemicrania. A 33-year-old female presented with a 5-year history of an acutely painful, stabbing headache dominating her left frontal and retro-orbital head regions. She described that the pain would last 10 to 15 minutes and occur five times daily. At the time of the headache, she noticed watering of her left eye and nasal stuffiness. She became restless and could not sit down. She had not noticed whether her attacks happened at a certain time of day or followed a certain pattern. She described having daily attacks for 6 months, with an intervening break of 10 to 12 months in which she would be headache-free.
Case 3. Primary cough headache. A 67-year-old male with no significant past medical history presented with a 4-month history of headache. He indicated that he developed a bitemporal headache with some dizziness when he coughed or during defecation. He did not have headache with sexual activity, exercise, or in relation to postural changes. There were no positive findings on the neurologic exam. Neuroimaging was normal.