Secondary headaches are caused by an underlying condition that results in head pain that can be just as severe as a migraine. In some cases, a secondary headache is a harbinger of a life-threatening issue. Often, it can make a primary headache worse.

Secondary headaches are different from primary headaches, which include migraines, tension, headaches, and cluster headaches. There is a set of diagnostic criteria to help healthcare providers determine a secondary headache. The criteria include specific features of the headache, along with the presence of the underlying issue.

Defining the Secondary Headache

As we said above, secondary headaches are so-called because they are secondary to another condition. An “ice cream headache” is a benign example of a secondary headache. Usually, the patient's medical history points to the cause. However, these types of headaches can mimic or exacerbate a primary headache.

The severity of the pain is not a distinguishing feature, and less than 10% of headaches seen in primary care are secondary headaches. 

Diagnostic Criteria

For a diagnosis of secondary headache, another disorder known to cause headaches must be observed. In most instances, the headache occurs around the time of the other disorder. There may be additional evidence of a causal relationship as well.

Secondary headaches should be significantly reduced or resolved within three months of successful treatment or spontaneous remission of the underlying condition. Also, the headache must be completely new in the situation, even if it resembles a type of primary headache.

A patient can actually have a diagnosis of both primary and secondary headache if: 

• The secondary cause is close in time to a change in the primary headache
• There is marked worsening of the primary headache
• There is evidence of another disorder that can aggravate a primary headache
• The secondary headache goes into remission after the other disorder is cured

For example, if someone suffers from migraines, and the migraines become more frequent after head trauma, that person would have both a primary and a secondary headache. Another common cause of secondary headaches is medication over-use for primary headaches. 

Distinguishing Between Primary and Secondary Headaches

To diagnose a secondary headache, the healthcare provider must take a thorough patient history and perform a physical exam. Some criteria are:

• It might be the first or the worst headache of the patient’s life.
• There must be a fundamental change in the pattern of a recurring headache.
• Cancer, HIV, and pregnancy may be the underlying causes of a secondary headache.
• Abnormal physical exams may uncover an underlying condition.

Physicians follow the SNOOP4 formula while diagnosing secondary headaches. SNOOP4 stands for:

• Systemic symptoms like fever, chills, night sweats, or unintentional weight loss.
• Neurological symptoms, such as weakness, numbness, trouble walking, confusion, seizures, or difficulty remaining awake or alert.
• Onset - it begins suddenly or abruptly. The pain may peak within one or two minutes, otherwise known as a thunderclap headache.
• Older age - the headache begins or progresses after the age of 50 (or less than 5 years old).
• Pattern change - a difference in frequency, severity, or character, different from previous headaches. 
• Progressive - the attacks worsen over time.
• Precipitated by exertion, like coughing, sexual activity, bowel movements, bearing down, or other activity.
• Positional worsening - the pain may be worse when you are upright or when you lie down.

Migraines account for just 16% of secondary headaches. The presence of a head injury is found in another 4% of cases. Exertion and vascular disorders cause about 1% of secondary headaches each. Subarachnoid hemorrhages cause less than 1%, and brain tumors account for only 0.1%.

Types and Causes

Head and Neck Trauma

While tension headaches are the most common cause of secondary headaches, they actually appear less frequently in severe head injuries. Women tend to have a higher disposition towards secondary headaches post-trauma. The elderly tend to have a slower recovery than others from head and neck trauma as well as an accompanying headache.

Classified types of secondary headaches caused by trauma include:

• Acute and chronic post-traumatic headache.
• Acute and chronic headache attributed to a whiplash injury.
• Headache attributed to traumatic intracranial hematoma.
• Headache attributed to other head and/or neck trauma.
• Post-craniotomy headache.

Infections of the Head or Neck

Certain infections tend to cause headaches, including pharyngitis, sinusitis, and meningitis.

Conditions Affecting the Brain and Coverings

Tumors, subdural hematomas, and hydrocephalus all cause secondary headaches.

Cranial and Blood Vessel Problems

Cranial and blood vessel issues may be diagnosed by the rapid and acute onset of headache, the presence of neurological symptoms, and the rapid remission of those symptoms. 

A hemorrhagic stroke may cause a headache, but the pain can be hidden by the focal neurological symptoms or a disturbance of consciousness. 

Non-vascular intracranial problems can cause a secondary headache. High or low cerebrospinal fluid pressure, noninfectious inflammatory disease, and brain tumors (intracranial neoplasms) can cause head pain. Epileptic seizures, a Chiari malformation type 1, and other non-vascular issues can underlie headaches.

Substance Abuse or Withdrawal

Exposure to toxins or environmental pollutants can cause a headache, as anyone who lives near a paper mill can attest.

Food allergies, caffeine, alcohol, therapeutic substances, and drug abuse can all cause you to develop a headache. Carbon monoxide poisoning, medication overuse, and medical withdrawals all cause headaches in some patients. In particular, withdrawing from drug dependence is very uncomfortable.

Other Causes

Secondary headaches come from many other issues such as dialysis, sleep apnea, fasting, hypothyroidism, disorders of the neck, eyes, ears, and jaw. The pain may be caused by a psychiatric disorder.

Children

Kids get secondary headaches from most of the same conditions as adults. Still, they can also get headaches from otitis media, optic neuritis, or glaucoma.

Conclusion

Secondary headaches are caused by a wide array of underlying conditions. Some are relatively benign, like headaches that occur when you don’t eat. Others are quite dangerous, such as those associated with a stroke. 

It's crucial to provide the physician with thorough answers about your health history and diagnoses. The physical exam is guided by your responses. There may be an emphasis on the optic nerve if your pain is around your eyes. Your blood pressure provides an important clue, especially since most people don't know when they have high blood pressure.

A thorough neurological exam may follow if particular symptoms are observed. Stiff neck, scalp tenderness, painful eyes, and fever can also provide the pathway to diagnosis.

A secondary headache is different from primary headaches, such as migraines. Something else is causing them. Treat that condition, and the headache should disappear.