“Dr. Google” will tell most people who go to him for advice, that a headache on one side is probably Migraine or cluster headache. Unless the user digs deeply into Dr. Google’s pages, they may make the unfortunate assumption that this is what they have.
Unilateral is the term used for pain in one side of the head, and it indicates that the pain doesn’t cross the midline/center line. It may be localized in a small to a large area of one side of the head, but does not in any way involve the other half of the head. It may be the entire side of the head.
The reality is that there can be many reasons for a unilateral headache, and only one of them is Migraine. The reason “Dr. Google” sends you to information about Migraine and cluster headache is because they are two commonly discussed causes for unilateral head pain, but far from the only headache disorders to consider.
There are several primary and secondary headache disorders that may result in unilateral head pain. If the patient isn’t seeing a headache specialist or physician familiar with ICHD-II diagnostic criteria, it’s much less likely that they will be made aware of alternative diagnoses for this type of pain. Non- specialists typically overlook less common disorders. Alternative diagnoses include:
Primary headache disorders
- Trigeminal Autonomic Cephalalgias (TAC’s) — cluster headache; paroxysmal hemicranias; short-lasting neuralgiform headache with conjunctival injection and tearing (SUNCT). These disorders include unilateral pain and autonomic symptoms (tearing, running nose, swelling, bloodshot eyes, drooping eyelids etc) on the same side as the pain. Patients with these disorders tend to be very active and agitated during an attack, often vocal, pacing or rocking, and frantic in their efforts for relief. This is in direct contrast to Migraine patients who tend to seek out a dark, quiet place to lie down and sleep. TAC patients are at increased risk of suicide.
- Hemicrania continua — a continuous, side-locked (rarely if ever changes sides) moderately severe headache with severe exacerbations. During exacerbations HC patients are often frantic for relief, similar to TAC’s. HC patients often have autonomic symptoms, but they tend to be less severe than TACS. HC is unique and is considered 100% responsive to a specific NSAID called indomethacin. HC patients tend to be labeled intractable, yet often find partial relief with other NSAIDs (close, but no cigar). Doctors familiar with the disorder recognize this tendency and perform a clinical trial of indomethacin to rule out the disorder. Sadly, HC is considerably under-diagnosed.
Secondary headache disorders
- Cervicogenic headache — a one-sided, nonthrobbing pain that originates in the neck. The pain may or may not be felt as radiating from the cervical spine area (C1 at the base of the skull through C7 located just above the shoulders) into the head. There may be neck pain and tenderness in focal areas (trigger points). Moving the neck or head, or pressing on points of the neck replicates the pain of cervicogenic headache. There is often a reduced range of motion of the head and neck, and muscle spasms. Symptoms of Migraine are also prominent in cervicogenic headache and include sensitivity to light and sound, nausea and vomiting. Diagnostic blocks are usually required to diagnose cervicogenic headache because its symptoms are so similar to Migraine and tension type headache.
- Arteritis — This unilateral headache is a symptom of an inflammatory process (often autoimmune) usually of the arteries of the external carotid artery or temple. Arteritis tends to be more common with age and responds to steroids within three days of the beginning of administration.
- TMJ Dysfunction — This type of pain can affect either one or both sides of the head and is often misdiagnosed as Migraine. Successful treatment of the dysfunctional joint resolves the head pain.
- Stroke – This headache is often unilateral and described as the worst headache of the patient’s life. Symptoms of stroke may sometimes mimic Migraine with aura, making diagnosis without imaging difficult in some patients.
This short listing is not to be considered in any way complete, but simply to give an example of some of the alternative diagnostic possibilities for unilateral headache. It’s interesting to note that over half of Migraineurs have pain on both sides of the head during an attack, and children suffering Migraine usually don’t have unilateral head pain, often making diagnosis more difficult for physicians who do not have a specialized interest in these disorders.