Abstract
Dear Sir We read with great interest the case series reported by Alvaro et al. on primary and secondary forms of the nummular headache syndrome (1). The authors emphasized a potential peripheral aetiology in two of their cases with a responsible structural lesion or cause. Because this headache disorder has been infrequently reported and its underlying pathophysiology remains speculative, we would like to report an additional case with unique aspects that stress the potential importance of central pain pathways in nummular headache.
A 40-year-old right-handed woman evaluated at the Montefiore Headache Center described a 3-year history of focal and well-circumscribed head pain in the left occipital region. The headache began without any precipitant. The affected area was perfectly oval, measuring 4 × 5 cm. The pain was described as a throbbing or dull ache, graded 2–7 out of 10 in intensity on a 10-point anchored scale. Individual attacks were associated with phonophobia and typically lasted 72 h, occurring up to 25 days per month. Any form of physical activity could aggravate the pain. She sought relief by lying down. She denied any numbness or tingling in the affected area, but it was occasionally tender to the touch.
Aside from sleep deprivation, the 2 days before and 1 day into her menses reliably triggered this headache in every menstrual cycle since onset. With this headache she would also be irritable and have low back pain perimenstrually. Her menses were somewhat irregular and she was known to have uterine fibroids. She had been pregnant four times, all preceding the onset of the headache. She never took oral contraceptive pills.
This patient also had a pre-existing history of episodic migraine with and without aura, although not menstrual-related migraine. These attacks had started several years prior to her current presentation, and these two headache types could coexist. Topiramate, triptans (zolmitriptan, frovatriptan, rizatriptan, sumatriptan), non-steroidal anti-inflammatory drugs and other analgesics had been ineffective for both headache types. However, the patient noted that when incidentally taking cyclobenzaprine 5 mg as needed for low back pain, her circumscribed headache intensity had diminished significantly. With an increased dosing regimen of cyclobenzaprine 5 mg three times daily, the intensity was reduced by at least 80%.
General physical and neurological examinations during an attack were normal except for hyperaesthesia in the affected painful area. Brain magnetic resonance imaging and computed tomography scan were normal. The patient's uncommon headache disorder was best characterized as a primary form of the nummular headache syndrome.
Our patient contributes to the small but growing literature on nummular headache and may add some useful considerations. First, this headache pattern has some similarities to migraine, including the duration of attacks, the associated symptom of phonophobia and aggravation by physical activity. Most notably, the patient seems to have menstrual-related nummular headache, a finding that to our knowledge has not been previously reported.
Menstrual-related headache is well reported in migraine, but has been documented infrequently in tension-type headache and, to an even lesser extent, in cluster headache and paroxysmal hemicrania (2–5). When larger series of patients with nummular headache are reported in future, perhaps an association between attacks of nummular headache and menses will be identified in a subset of women affected with this disorder. The role of oestrogen in menstrual-related headache has been postulated to affect both peripheral and central nociception. Declining serum oestrogen levels may increase pronociceptive effects (increased glutamatergic tonus and excitability of trigeminal afferents) and decrease antinociceptive effects (decreased serotonergic, opiatergic and GABAergic tonus, as well as decreased glutamate reuptake), and by these mechanisms may be relevant to nummular headache as well (6).
The response of this patient's nummular headache to cyclobenzaprine may also indicate important central mechanisms of pain in this disorder. Cyclobenzaprine, a centrally acting muscle relaxant that is structurally similar to the tricyclic antidepressant amitriptyline, may function by antagonizing serotonin receptors in the central nervous system (7). It has been used successfully in some patients with chronic tension-type headache (8). On a related note, a small series of patients with nummular headache from our institution have responded well to tricyclic antidepressants (9).
The cases presented by Alvaro et al. (1) help confirm the concept of a secondary form of nummular headache, thus expanding the clinical spectrum of this syndrome. Future research on the primary and secondary forms of this disorder will require a standardized review of the literature in order to define the clinical features, differentiate it from other existing headache disorders, and give evidence-based treatment recommendations. Furthermore, the pathophysiology of nummular headache may be better defined by functional neuroimaging, a procedure that has shed light on the biology of other primary headache disorders.