Hemicrania continua (HC) is a rare primary headache disorder characterized by continuous, unilateral pain accompanied by autonomic features. Despite its distinct clinical profile, HC often poses diagnostic challenges, leading to underrecognition and misdiagnosis. This review provides a comprehensive overview of the clinical features, diagnostic criteria, pathophysiology, and management strategies for hemicrania continua based on current literature and clinical experience.

Introduction: Hemicrania continua is a primary headache disorder characterized by unremitting unilateral pain with superimposed exacerbations of severe intensity. Understanding the characteristic features and diagnostic criteria for HC is essential for accurate diagnosis and effective management.

Epidemiology: Hemicrania continua is considered a rare headache syndrome, comprising a small percentage of patients seen in headache clinics. The prevalence of HC in the general population remains uncertain, with estimates ranging from 0.1% to 0.5%. It affects both genders equally and typically manifests in adulthood, although cases have been reported in children and adolescents.

Clinical Features: The hallmark feature of hemicrania continua is continuous, unilateral headache of moderate intensity, with exacerbations of severe pain occurring episodically. The pain is typically localized in the orbital, temporal, or frontotemporal region and may be associated with autonomic symptoms such as ptosis, miosis, conjunctival injection, lacrimation, nasal congestion, and rhinorrhea. The presence of both continuous and exacerbating pain distinguishes HC from other headache syndromes.

Pathophysiology: The exact pathophysiology of hemicrania continua remains incompletely understood. Proposed mechanisms include central sensitization, neurovascular dysfunction, and abnormal activation of trigeminal autonomic reflex pathways. The role of the hypothalamus in regulating pain modulation and autonomic function has also been implicated in the pathogenesis of HC.

Diagnosis: The diagnosis of hemicrania continua is primarily based on clinical criteria outlined in the International Classification of Headache Disorders (ICHD). Key features include unilateral headache of continuous moderate intensity with exacerbations of severe pain lasting minutes to days, accompanied by ipsilateral autonomic symptoms. Response to indomethacin, a nonsteroidal anti-inflammatory drug, is considered a diagnostic hallmark, with complete resolution of symptoms confirming the diagnosis.

Management: Indomethacin is the treatment of choice for hemicrania continua, typically providing complete or partial relief of symptoms within hours to days. However, long-term use of indomethacin may be limited by gastrointestinal side effects and potential adverse effects on renal function. Alternative pharmacological agents such as gabapentin, topiramate, and melatonin have been investigated as adjunctive or alternative therapies in indomethacin-refractory cases. Neuromodulatory approaches including occipital nerve stimulation and deep brain stimulation may be considered in severe, refractory cases.

Conclusion: Hemicrania continua is a rare but debilitating primary headache disorder characterized by continuous unilateral pain interspersed with exacerbations of severe intensity. Early recognition and prompt initiation of indomethacin therapy are essential for achieving optimal outcomes and improving patient quality of life. Further research is needed to elucidate the underlying pathophysiological mechanisms and explore alternative therapeutic options for hemicrania continua. Collaboration between headache specialists and neurologists is crucial for comprehensive management and patient-centered care.