Deciphering ICHD-3: A Practical Approach to Primary vs. Secondary Headaches

Navigating headache diagnostics in a clinical setting requires a clear framework to distinguish benign functional conditions from life-threatening secondary etiologies. The International Classification of Headache Disorders (ICHD-3) organizes headaches into three primary domains:

• Primary Headache Disorders: Conditions where the headache itself is the disease entity, including Migraine, Tension-Type Headache (TTH), and Trigeminal Autonomic Cephalalgias (TACs) such as Cluster Headache.

• Secondary Headache Disorders: Headaches caused by underlying pathology, ranging from head trauma, cranial or cervical vascular disorders (e.g., Subarachnoid Hemorrhage, Giant Cell Arteritis), non-vascular intracranial pressure alterations, infections (e.g., Meningitis), to homeostasis disruptions and substance withdrawal.

• Painful Cranial Neuropathies & Other Facial Pains: Lesions involving cranial nerves, such as Trigeminal Neuralgia and Occipital Neuralgia.

When assessing a patient, clinicians must evaluate attack frequency and duration. Episodic primary headaches typically manifest as discrete paroxysmal attacks lasting under 4 hours or isolated episodes. Conversely, chronic daily or near-daily headaches lasting more than 4 hours per day—such as Chronic Migraine, Chronic TTH, Hemicrania Continua, and New Daily Persistent Headache (NDPH)—require careful assessment for potential medication overuse.