Observational Prospective Study on the Presence of Typical Migraine Features in Nummular Headache Patients: The Numamig Study

Background: Nummular headache (NH) is a primary headache included in the International Classification of Headache Disorders (ICHD) characterized by a well delimited superficial pain, with sharp border, felt in a rounded or elliptical 1-6 centimeters area. Pain might be continuous or intermittent. The key feature of nummular headache is the fixed superficial topography. The real nature of this condition is still a matter of controversial. Some authors defend it as a specific condition with a particular pathophysiology; whereas others consider that it might be a localized form of migraine with a shared phenotype and pathophysiology. Among the arguments that defend its existence as a differentiated entity we include: the older age of onset, the fixed and localized pain without pain in other territories, presence of trophic changes, the localized abnormality in pressure pain threshold determination, the description of secondary cases, the description of posttraumatic cases or the specific therapeutic response. On the other hand, in some cases hypersensitivity to stimuli has been described, other typical migrainous symptoms such as nausea or vomiting might be present, and some patients respond to triptans or other migraine prophylactics. Information is scarce about the presence of prodromes, postdromes or family history of migraine. Moreover, little is known about NH pathophysiology, some studies suggest an impairment in superficial sensory fibers because a localized alteration of pressure-pain threshold. No imaging or laboratory studies have been done so far. This is a proof of concept study. The aim is to analyze if patients with a definite NH diagnosis according to ICHD present any shared epidemiological, clinical or therapeutical features with migraine. Hypothesis: Nummular headache might be a specific condition or it might share migraine biologic features. The detailed description of it might help to clarify whether if NH is a single entity or a focal presentation form of migraine. Objective: To describe the presence of typical features of migraine in a cohort of NH patients, including family history, epidemiology, clinical description, presence of prodromes or postdromes and response to treatment. Methods: The study has an observational analytic design following the Strengthening the Reporting of Observational in Epidemiology (STROBE) guidelines. Patients with definite nummular headache diagnosis according to The International Classification of Headache Disorders1 will be invited to participate. The study will be conducted in the Headache Unit of Hospital Clinico Universitario de Valladolid, a third level hospital sited in Valladolid, with a reference population of 280.000 people. Intervention: The study will be divided into different sections: 1. Family history of headache and in particular, migraine. 2. Epidemiology of NH patients. 3. Clinical phenotype and pattern of the headache. 4. Associated symptoms, presence of prodromes and postdromes. 5. Physical examination. 6. Prior treatment use, tolerability and response. Selection of participants: Recruitment will be recruited by a non-probabilistic sampling method by convenience and by formal invitation if they are included in the clinical registry of the Headache Unit of the Hospital Clinico Universitario de Valladolid. In the first visit participants will be examined by a neurologist with experience in headache disorders and NH diagnosis will be reviewed. Patients will be invited to participate into the study and they will provide and sign informed consent form. They will be instructed and trained to complete the prospective headache diary during 14 days. A follow up visit will be done within 15 to 30 days to review the data and analyze possible sources of bias.