|3||CLUSTER HEADACHE AND OTHER TRIGEMINAL AUTONOMIC CEPHALALGIAS||G44.0|
|Coded elsewhere||4.7 Hemicrania continua|
Primary or secondary headache or both?
When a headache with the characteristics of a trigeminal autonomic cephalalgia (TAC) occurs for the first time in close temporal relation to another disorder that is a known cause of headache, it is coded according to the causative disorder as a secondary headache. When a pre-existing TAC is made worse in close temporal relation to another disorder that is a known cause of headache, there are two possibilities, and judgment is required. The patient can either be given only the TAC diagnosis or be given both the TAC diagnosis and a secondary headache diagnosis according to the other disorder. Factors that support adding the latter diagnosis are: a very close temporal relation to the disorder, a marked worsening of the TAC, very good evidence that the disorder can cause or aggravate the TAC and, finally, improvement or resolution of the TAC after relief from the disorder.
The trigeminal autonomic cephalalgias share the clinical features of headache and prominent cranial parasympathetic autonomic features. Experimental and human functional imaging suggests that these syndromes activate a normal human trigeminal-parasympathetic reflex with clinical signs of cranial sympathetic dysfunction being secondary. Hemicrania continua, whose cranial autonomic features are less constant, is to be found under 4. Other primary headaches.