Chronic daily headache (CDH) is a label for a heterogeneous group of headache disorders that can be a management challenge for busy physicians. Patients with CDH account for most referrals to headache specialists.¹ Disagreement about the clinical groupings and diagnostic criteria for these types of headaches has contributed to the difficulty in treating these patients.

The International Classification of Headache Disorders² identifies 24 types of chronic headache. Many of them are rare conditions that are mainly of interest to researchers and headache specialists; some, however, are not uncommon.

Part of the confusion concerning the classification of headaches has arisen over the use of the term “chronic” when applied to headache. The International Classification² clarifies this terminology.

Primary episodic headaches, such as migraine or tension-type headaches, are classified as chronic when the attacks occur on more days than not over a period of at least three months. In terms of pain, however, “chronic” denotes persistent pain over a period of at least three months. This latter definition is retained in the headache field for secondary headache, in which underlying pathology or systemic disease is the cause of the headache. To the non-headache specialist, this terminology may seem like splitting hairs. But in an excellent article³ on CDH in this issue, Dr. Maizels draws attention to these points and emphasizes the importance of accurate diagnosis in dealing with patients who have these types of headache.

Studies in the United States⁴ and Europe⁵ indicate that 4 to 5 percent of the general population have primary CDH.⁴ The leading cause is chronic tension-type headache (53.7 percent), followed by chronic migraine (31.7 percent).⁵

Chronic migraine, also known as transformed migraine, is a new headache diagnosis introduced by the International Headache Society. Typically, the patient reports gradual worsening of migraine over a period of months or years. Headache pain and associated symptoms of photophobia, phonophobia, and nausea are usually less severe but become less responsive to treatment, causing the patient to overmedicate. Chronic tension-type headache, which is more common than chronic migraine, is encountered less frequently in family practice patients. These headaches are diffuse or bilateral, and frequently involve the posterior head and neck.

The overuse of analgesics, barbiturates, opioids, triptans, or ergots may convert both migraine and tension-type headaches into CDH. Drug-induced CDH is thought to be caused by drug withdrawal between treatments. This is known as rebound headache, in which a vicious cycle of increased drug use follows. There are no reports of spontaneous improvement of rebound headache.

Because of the insidious nature of CDH, physicians should remain on the alert when patients complain of an increasing frequency of headache and make increased demands for medication. Many patients with headache do not realize that excessive or frequent self-treatment may perpetuate or exacerbate headache. Skillful management is needed when withdrawing pain medication and controlling the subsequent headache exacerbation.

Long-term CDH prognosis is variable. In the short term, patients treated aggressively with detoxification where appropriate, and antidepressants or antiepileptics as indicated, generally improve. Attention should be paid to psychiatric comorbidities. Anxiety, depression, and bipolar disease are more frequent in patients who have migraines than in non-migraine control subjects. It is believed that migraine and depression share the same etiologies, rather than the depression resulting from the demoralizing effect of repeated migraine attacks.⁶ Some features of comorbid depression show improvement when the cycle of CDH is broken.⁷ Maizels³ correctly emphasizes the importance of screening for depression in all patients with CDH. In some patients, recognition of the rebound mechanism itself can be therapeutic.