Migraine and, to a lesser degree, TTH are well-studied and described in the pediatric literature, but little is written on many others, especially rare primary headache disorders and the uncommon variants and complications of common headache disorders in children and adolescents. Except for migraine, the three editions of the International Classification of Headache Disorders (ICHD-1, ICHD-2 and ICHD-3), provided definitions and criteria for the diagnosis of all headache disorders derived from studies on and experience in adult patients [4-6]. It is conceivable that the clinical presentations of most, if not all, primary headache disorders in children can be different than those in adults [7]. The differences can be due to the inherent nature of the disease itself, neurodevelopmental factors, biopsychosocial influences of the disease, life-style and education, and also children’s response to pharmacologic and non-pharmacologic therapies. Therefore, studies on uncommon headache disorders in children and adolescents are badly needed in order to better define the conditions and inform management decisions.

Headache disorders are classified on the basis of etiology into primary (no other underlying cause), secondary (when headache is a manifestation of another disorder) and undetermined etiology (Box I). Headaches are also sub-classified on the basis of frequency of attacks and duration of the headache disorder into episodic (less than 15 days per month) or chronic (attacks occur on at least 15 days per month over at least three consecutive months). Migraine is further sub-classified according to clinical features (different types of migraine) and trigeminal autonomic cephalalgias (TACs) are sub-classified on the basis of attack duration.

In the absence of diagnostic tests and biomarkers, the diagnoses of primary headache disorders are based on the clinical features and globally acceptable definitions and diagnostic criteria. A focused and detailed clinical history is essential in assessment of children with headache in order to make a positive diagnosis, and appropriate classification. Making the right diagnosis allows explaining the condition to the child and the family, making a rational decision on investigations if needed, offering the most appropriate treatment options and helps in predicting prognosis. Essential elements of clinical history, general examination and neurological exami-nation are summarized in Table I and management workup may follow the steps as shown in Fig. 1.

The severity of pain is best assessed by its effects on behavior and activities; severe headache stops all activities during attacks, moderate headache stops some but not all activities, and mild headache dose not interfere with normal daily activities. Absence of symptoms between attacks and complete return to normal self is an important feature of primary headache. Secondary headaches should be suspected and considered if red flags are detected on the clinical history, and physical and neurological examinations (Box II).

The diagnosis of common primary headache disorders such as migraine and tension-type headache can be made confidently on clinical history, normal examination, absent red flags and on the application of the ICHD-3 criteria. Other less common headache disorders may cause difficulties in diagnosis and management and will be the subject for this review.

Exploring and addressing the concerns of patients and their families are the first important steps in successful management. Advice on healthy life style – regular meals, sleep, exercise and rest may reduce impact and improve coping with headache.

For acute treatment, simple analgesics should be used in appropriate dosages and as early as possible after onset of headache. Children should avoid taking painkillers on more than three days per week in order to avoid medication overuse headache (MOH). Triptans can also be given in acute migraine attacks in accordance with local license and regulations and with similar precautions to avoid MOH.

Evidence-based recommendation in the prevention of migraine can be hard to find with conflicting evidence, however treatment with propranolol, topiramate, flunarizine and amitriptyline can be considered on individual basis. Specific treatment for rare headache disorders will be discussed separately.

Migraine is a common disorder with a prevalence of around 10% in schoolchildren [1], and chronic migraine (CM) is a subtype of migraine. The diagnosis of CM is made when headache occurs on at least 15 days per month on at least 3 consecutive months, of which at least on 8 days per month the headaches are those of migraine [6].

Migraine may present as CM from the onset, but it can also evolve over a period of time in children with episodic migraine. It is estimated that about 2% of adolescents suffer from CM and at least half the patients overuse medication; simple analgesics or anti-migraine drugs such as sumatriptan [8]. CM is more common in girls than boys and more prevalent in adolescents than in younger children. CM has a significant impact on the child’s quality of life, school attendance and educational attainment as compared to children with episodic migraine and control healthy children [8].

The management of children with CM can be difficult and, ideally, needs a multidisciplinary approach and a positive contribution from parents and guardians, clinical psycho-logy services, education and school teachers and also from school nurses. Investigations are not necessary except in presence of red flags or new abnormalities on neurological examination. An individual migraine management plan agreed upon by the child, the parents and members of the multi-disciplinary team (MDT) promotes better manage-ment of headache at home and at school and may reduce impact on education and quality of life.

Medical management starts with reducing the risk of medication overuse and treatment of MOH when present. Pain killers should, therefore be avoided as they have a limited role. Preventive drugs aim to reduce the frequency and the severity of migraine attacks and to improve the quality of life. Several medications are used but with sometime, a conflicting evidence for their effectiveness. Amitriptyline, with and without cognitive behavioral therapy (CBT), topiramate, flunarizine and botox are commonly offered to patients [9-11]. Greater occipital nerve block and botox injections are possible future management options. Calcitonin-gene related peptide (CGRP) monoclonal antibodies are shown to be successful in migraine prevention in adults, but still awaiting trials and licensing in children.

Prognosis: The prognosis and the long-term course of CM have not been well studied in children, but the impact on quality of life is a consistent feature and studies showed reduced educational attainment and earning power during adult life [12].

Hemiplegic migraine (HM) is a form of migraine with motor aura and depending on presence or absence of other affected family members; it is divided into familial hemiplegic migraine (FHM) or sporadic hemiplegic migraine (SHM). FHM is sub-classified according to the underlying genetic mutation; FHM1 is associated with a mutation on the CACNA1A gene, FHM2 on the ATP1A2 gene, FHM3 on SCN1A and FHM (other loci) when no genetic mutation can be found despite the familial occurrence of the disease.

The prevalence of HM is not known, but is considered rare. About 2% of patient seen at a specialist children headache clinic have HM [13]. Girls are more commonly affected than boys and its peak incidence is during adolescence.

The clinical presentation of HM can be distressing to the child, frightening to the family and can pose a dilemma in diagnosis for clinicians. Attacks can be triggered by minor head trauma and followed by complex aura; a combination of visual, sensory, speech and motor symptoms. The headache that follows can be severe and is often associated with intense nausea and vomiting that may lead to confusion and dehydration.

A recent study on a cohort of 46 children with HM showed that children present with fewer non-motor auras than adults and the first attack may be preceded by transient neurological signs and symptoms especially in early childhood [14]. The attacks can last over 1-2 days and children will be, invariably, investigated with neuroimaging to rule out space occupying lesions, intracranial bleeding or arterial ischemic strokes. Investigation will always be necessary, especially on the first presentation as the diagnosis, as defined by (ICHD-3), can only be made after at least two fully reversible attacks.

Distinguishing HM from stroke can be difficult on clinical features alone as they share many symptoms. Standard MRI of the brain may not be helpful and specialist cerebral perfusion studies using functional MRI and arterial spin labeling (ASL), only available at limited centers, may demonstrate areas of cerebral hypoperfusion soon after onset of symptoms and hyperperfusion 12-14 hours after onset. The changes in perfusion are not limited to the territories of the main cerebral arteries but they are evident across the boundaries suggesting neural rather than vascular basis of this phenomenon [15,16].

Treatment of acute attacks once the diagnosis is established should aim at reassuring the child and parents, providing effective pain relief, hydration and monitoring of symptoms. Simple analgesics (paracetamol 10-20 mg/kg or ibuprofen 7.5-10 mg/kg) are the preferred options. The use of triptans is currently not recommended as all clinical trials excluded children and adults with HM and there is no evidence of their safety in children and adolescents. The exclusion from trials was based on the theoretical risk of triptans exacerbating cerebral vasoconstriction and causing cerebral infarction.

Care should be taken to prevent dehydration by encouraging oral fluids, but intravenous fluids may be necessary. Antiemetic medications such as metoclopra-mide or ondansetron may also be needed.

Preventative treatment may be necessary if attacks are prolonged, frequent or causes distress to child and parents. Topiramate, amitriptyline and flunarizine in particular are good treatment options.

Prognosis: Counseling of patients should take into account the known natural history of the disease, which is characterized by periods of remissions and relapses. The attacks of HM tend to be frequent and severe during adolescence and also in late adult life with periods of remission in between. A follow up of eight family members for a mean period of ten years showed the disease to be clinically stable [17]. Children with FHM1 due to associated CACNA1A gene mutation have an increased risk of progressive ataxia in late adult life and children with FHM3 due to SCN1A mutation are at a higher risk for epilepsy.

Thunderclap headache (TH) is a term given to describe sudden severe headache that reaches its peak intensity within seconds or minutes and persists for hours. TH may become recurrent over several weeks if untreated. TH is a secondary headache in most cases and a diagnosis of primary TH should only be made after full, appropriate and timely investigations including neuroimaging. The prevalence of TH in children and adolescents is not known and it is rare in pediatric clinical practice. Cases reported in children are mostly secondary to sinus venous thrombosis [18].

The clinical features of TH in children are probably similar to those in adults. The clinical picture is usually dominated by the abrupt onset of the headache and its severe intensity described by patients as the most severe headache they have ever experienced, prompting them to seek urgent medical advice and assessment. The headache attacks can be brief, but repetitive. Although the criteria for the diagnosis of TH in ICHD-3 (Box III) are that of primary TH, it is always necessary to exclude underlying intracranial vascular disease.

Secondary TH: TH may be the presenting symptoms in patients with several intracranial vascular disorders. The most common causes of TH in children and adolescents are intracerebral haemorrhage, cerebral venous thrombosis, subarachnoid haemorrhage with or without ruptured arterial aneurysms and reversible cerebral vasoconstriction syndrome (RCVS). Secondary TH may not be immediately distinguishable from primary TH and therefore full neurological examination and measurement of arterial blood pressure are mandatory. Prompt recognition and urgent appropriate assessment start at emergency department in order to avoid life-threatening complications [19].

Investigations at presentation should include brain MRI and MR angiography. Other investigations should also include CSF opening pressure, CSF microscopy, culture, protein and glucose (paired with blood glucose) and examination for xanthchromia at appropriate time interval from presentation. MRA may need to be repeated if RCVS is highly suspected, as vasoconstriction may not be apparent in the early stages of the disease.

Treatment aims to relieve symptom while addressing the management requirements of the underlying condition.

Chiari malformation is a congenital anomaly of the posterior cranial fossa characterized by crowding of its contents, a caudal displacement of the cerebellar tonsils and brainstem through the foramen magnum and an associated expansion of the CSF spaces in the cervical and possibly the thoracic spinal canal creating a static or progressive syrinx. Chiari malformation is classified into types 1-4 depending on the degree of malformation, the extent of cerebellar and brainstem herniation into the foramen magnum, cerebellar hypoplasia, syringomyelia, obstruction of CSF flow and presence of an encephalocele.

Chiari malformation type 1 (CM1) is the most common form and it is asymptomatic in the vast majority of cases. In CM1, there is mild to moderate crowding of the posterior fossa and a descent of cerebellar tonsils between 5-10 mm below the foramen magnum with no or a very small syrinx. It is commonly reported as an incidental finding in about 1% of children and young people undergoing brain and spine MRI [20].

Headache due to CM1 is described in the ICHD-3 as brief episodes lasting less than 5 minutes of occipital or suboccipital pain, precipitated by cough or Valsalva maneuver and it remits after successful treatment of CM1 [6]. It is important to keep in mind that children with CM1 may also complain of other types of headache such as migraine and tension-type headache, and they should not be confused with CM1 headache. On rare occasions, children with CM1 may present with other symptoms related to brainstem or cerebellar dysfunction including visual disturbances, dysphonia, dysphagia, sleep apnea, incoordination and sensory disturbances.

The diagnosis of CM1 is usually made on the sagittal MRI of the brain and the cervical spine. The management of children with CM1 is non-surgical in most patients after discussion with a neurosurgeon and a neuroradiologist. Medical management should include appropriate manage- ment of the pain symptoms and a follow up imaging over a period of time to confirm the non-progressive nature of the malformation and the size of the syrinx, if present, in particular [21].

Surgery is only recommended for patients with features suggesting brainstem or cerebellar compression, a large or progressive syringomyelia or with a poorly controlled, typical CM1 headache disorder. A single center experience in the surgical treatment of children with CM1 over 25 years showed that children with typical CM1 headache who were treated with foramen magnum decompression (FMD) plus duraplasty achieved a greater improvement in their headache than those treated with FMD alone [22].

Primary stabbing headache (PSH) is an uncommon syndrome, also called ice-pick headache, characterized by very short attacks. While ICHD-2 states that pain is confined exclusively to the trigeminal territory, it has been accepted in ICHD-3 to cross beyond the boundaries of the trigeminal nerve and can be unilateral or bilateral in location (Box IV). The typical stab lasts a few seconds; however, attacks lasting up to 15 minutes in children and adolescents have been reported [23].

Although the exact prevalence of PHS in the pediatric population is unknown, 4-5% of children referred to headache centers have PSH [23-25]. In an Italian study, 12.4% of children with headache younger than 6 years had PSH [26]. Girls and boys are equally affected, though in adults PSH is more common in females [27]. Other primary headaches; migraine and TTH may coexist with PSH in children [28-30]. Associated symptoms, such as photo-phobia, phonophobia, nausea, and dizziness, have been described in 20-50% of patients. Absence of autonomic symptoms is the main feature that differentiates PSH from trigeminal autonomic cephalalgias.

The pathophysiology of PSH is unknown, but spontaneous firing of trigeminal fibers or abnormalities of the descending pain control have been suggested as possible mechanisms [27]. The relatively higher prevalence of PSH in younger children suggests that PHS may be a precursor of migraine/TTH [16].

Treatment of PSH in children is often not necessary, unless the stabs are very frequent and interfere with normal activities. Evidence for any medications in the treatment of PSH is lacking, but indomethacin may offer an excellent relief of pain when given in a dose of 25 mg three times per day for 6-8 weeks alongside omeprazole for gastric protection. Melatonin, amitriptyline, propanol, and COX2-inhibitors were effective in adults and may be used in children [27].

Trigeminal Autonomic Cephalalgias (TACs) are also uncommon, especially in pediatric age. However, they must be considered even in young children, in order to offer the appropriate treatment. They include cluster headache (CH), Paroxysmal hemicrania (PH), Hemicrania Continua (HC), and Short-lasting Unilateral Neuralgiform headache attacks with Conjunctival injection and Tearing (SUNCT) or with cranial autonomic symptoms (SUNA). Table II presents the characteristics and the differential diagnosis of these conditions.

The prevalence of cluster headache (CH) in the pediatric population is around 0.1% [31]. CH is characterized by severe and sometimes excruciating unilateral pain, mainly in the orbital, supraorbital, and/or temporal region, lasting 15-180 minutes and recurring up to 8 attacks per day. Attacks are often associated with restlessness and/or ipsilateral autonomic symptoms, such as conjunctival injection, lacrimation, nasal congestion, rhinorrhea, eyelid edema, forehead and facial sweating, miosis, and ptosis. The usual presentation of CH is that of recurrent bouts of headache, each bout consisting of several distinct headache attacks. In episodic CH, the bouts of headache last from 7 days to 1 year, and are separated by headache-free periods without treatment of at least 3 months. In chronic CH, the headache-free period between bouts is shorter than 3 months. It has been recently suggested that the attacks can be shorter and less frequent in children than in adults and restlessness can be more difficult to demonstrate [7,32].

CH is more common in children over 10 years of age, but it has been reported in children younger than 6 years of age [33,34]. Complex genetic factors are probably involved in CH etiology [35,36]. However, it was noted that there is a low prevalence (9%) of CH in the relatives of young patients [34]. Environmental factors such as high exposure to second hand smoking has been suggested as a risk factor for CH development [34,37].

Treatment: Treatment of acute attacks in children and adolescents consists of administering, as early as possible after onset, either sumatriptan 10 mg or zolmitriptan 5 mg (as nasal spray), which are the only licensed triptans for adolescents 12-18 years of age in Europe as well as high flow 100% oxygen at 12-15 L/min with a rebreathing mask [38].

Paroxysmal hemicrania (PH) is characterized by short lasting (2-30 min), multiple and unilateral pain attacks, with a typical attack frequency of more than 5 per day. Pain is commonly associated with ipsilateral cranial autonomic symptoms. PH is defined as episodic when attacks last from 7 days to 1 year and are separated by time intervals longer than 3 months. In chronic PH, the attack has to last more than 1 year without interruption or with pain-free intervals shorter than 3 months. In children, PH can be atypical with bilateral pain, attack duration longer than 30 minutes and attack frequency less than 5 per day making it difficult to differentiate from CH [7,40,41].

PH responds well to treatment with indomethacin, making it a good therapeutic first line option in all patients with unilateral short-lasting pain, associated with cranial autonomic symptoms.

Hemicrania continua (HC) is characterized by continuous unilateral headache with exacerbations of moderate or greater intensity for at least 3 consecutive months. As in PH, cranial autonomic symptoms ipsilateral to pain and/or sense of restlessness are needed for the diagnosis. The response to indomethacin should be complete, but can be variable in some children. Only a few pediatric cases of HC have been published with one patient responding to treatment with Botulinum toxin A [42,43].

These short-lasting neuralgiform attacks, lasting from 1 to 600 sec, involve the trigeminal territory unilaterally. The attacks can be isolated or can recur in series. Pain is associated with conjunctival injection and/or tearing in SUNCT or other cranial autonomic symptoms, such as nasal congestion and/or rhinorrhea, eyelid edema, forehead and facial sweating, miosis, and/or ptosis in SUNA. Only four cases of pediatric SUNCT (3 idiopathic and 1 symptomatic) have been described thus far [7].

Pediatricians are familiar with the diagnosis and treatment of common headache disorders in children and adolescents. Awareness of the different types of atypical or rare headache disorders allows better assessment and a more successful management. Learning points related to these disorders are detailed in Box V.

Diagnosis should be based on the recognized clinical criteria of the ICHD. Investigations to exclude serious underlying neurological disorders may be necessary, but should be interpreted with caution, in order to avoid over-diagnosis of incidental findings such as Chiari malformation 1. Chronic migraine can be associated with adverse impact on quality of life and can be difficult to manage. Hemiplegic migraine may pose diagnostic difficulties making investigations necessary including MR angiography, especially at first presentation. Trigeminal autonomic cephalalgias and stabbing headache are relatively rare in children, but with the correct use of diagnostic criteria, management plans with appropriate treatment options and realistic expectations, it is possible to address the patient needs.

Contributors: All authors contributed equally and approved the final manuscript.

Funding: None; Competing interest: None stated.

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