The Secondary Headaches: Introduction

Jes Olesen

Nabih M. Ramadan

Secondary, according to Webster, is a term used in medicine to indicate “dependent or consequent upon other diseases.” The International Classification of Headache Disorders (ICHD-II) categorizes headaches as primary if not caused by another disorder and as secondary if caused by another disorder. Thus, conditions such as central nervous system infections or trauma cause secondary headaches (headache is a symptom of the underlying medical illness), whereas the headaches of migraine are primary. It is important to underline that the term primary does not mean nonorganic or idiopathic or without a neurobiologic basis. The causes of secondary headaches are numerous. In ICHD-II they have been ordered in eight groups (1) (Table 104-1). Alcohol overuse (hangover), infections, trauma, and fasting are among the most common causes of secondary headache (2,3). Often, the characteristics of secondary headaches overlap with those of primary headache disorders, which might pose significant diagnostic difficulties.

CHARACTERISTICS OF SECONDARY HEADACHES

The exact characteristics of many secondary headaches are not sufficiently documented. The new standard for diagnostic criteria for secondary headaches (Table 104-2) allows a characterization of the headache features of all secondary headaches. Some secondary headaches (e.g., postlumbar puncture headache) have distinctive characteristics that would be essential to the diagnosis. Such unique characteristics are listed. Systematic documentation of secondary headache characteristics, as now required in the revised classification, will undoubtedly facilitate future nosologic headache studies.

Headache is one of the most common presenting symptoms to a physician, and an identification of differentiating headache characteristics may aid in arriving at the correct diagnosis. Such situations are quite important when headache is a cardinal symptom of the underlying disorder (e.g., arteritis, arterial dissection, cerebral venous thrombosis, increased intracranial pressure, low spinal fluid pressure, hypophyseal neoplasms, and meningitis). In other instances, headache is not essential to the diagnosis or management, and a detailed etiologic classification is not worthwhile. An example would be a subclassification of headaches attributed to infection on the basis of the causative pathogen (e.g., virus, bacteria, etc.). It should be borne in mind, however, that criterion A of the ICHD-II can stimulate research that may indicate differential headache characteristics with different infections. Then, a thorough knowledge of the headache characteristics will have farreaching diagnostic implications.

CAUSALITY IN SECONDARY HEADACHES

A close temporal relation is the most important, and sometimes the only, reason for causality. In acute-onset headaches, a temporal relationship usually is established easily and causality is inferred accordingly. On the other hand, it may be quite difficult to establish a temporal relationship in chronic conditions associated with headache. In such instances, removal of the putative cause and resolution of the headache establishes the link (criterion D, Table 104-2). For example, a patient suffered from migraine
attacks for years, and a cerebral arteriovenous malformation or meningioma is discovered during the evaluation for increasing headache attack frequency. The answer to the causality issue in this case can be established if the headache greatly improves or disappears after a successful operation. In other words, diagnostic criterion D is fulfilled (Table 104-2). Alternatively, if the headache does not improve or disappear and a clear temporal relationship cannot be established, a probable diagnosis of the secondary headache can be given (see Chapter 2).

TABLE 104-1 The Secondary Headaches