The SUN Also Rises

This issue of Headache Currents contains two masterful clinical reviews on short-lasting unilateral headache attacks by two of the leading experts on these disorders, Drs. Raphael Benoliel et al and Anna Cohen. The International Classification of Headache Disorders (ICHD-3) Beta places the two previously proposed trigeminal autonomic cephalalgias (TACs), short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA) under the rubric of short-lasting unilateral headache attacks. The acronym for these headache attacks is not yet established. Dr. Benoliel refers to them as SUNHA; Dr. Cohen refers to them as SUN. I personally prefer SUNHA, although the puns are better with SUN. The clinical spectrum of SUNHA is relatively wide. Originally described to Dr. Otto Sjaastad et al. in 1989, Dr. Cohen first called attention to the different patterns of stabs seen in attacks in her classic paper with Drs. Manjit Matharu and Peter Goadsby published in Brain in 2006. Her current paper is an overview, beginning with clinical features, moving to differential diagnosis and the risk of missing secondary causes such as pituitary tumors, MS, space-occupying lesions, and other vascular causes, and ending with a thorough discussion of treatments, from medication to neuromodulation and surgery. This is a go-to paper for SUNHA reference. I first heard Dr. Benoliel lecture on the difficulty in telling SUNHA from classical trigeminal neuralgia (CTN) at one of Dr. Joel Saper’s Michigan Head Pain and Neurological Institute’s Annual CME Updates in Headache and Pain Management conferences. I realized how I could have missed the diagnosis and never been aware. For this reason, I asked Dr. Benoliel to write a careful review primarily on this issue, and the result is remarkable. As he and his colleagues state, “Shared clinical signs [between SUNHA and CTN] include severe, unilateral trigeminal pain that is often triggered by innocuous stimuli and accompanied by a dull persistent background pain. Recent reports on trigeminal neuralgia cases with atypical features such as autonomic signs and prolonged attack duration further blur the clinical distinction between CTN and SUNHAs. . . Are the similarities greater than their differences? If so, this may reflect a spectrum of disease ranging from typical CTN attacks to typical SUNHAs with a mixed phenotype in the middle. In this review, we will summarize the overlap between these entities and contrast the pathophysiology and treatment approach.” Dr. Cohen also describes the differential diagnosis challenge in the section of her paper entitled, “SUNCT, SUNA, and Trigeminal Neuralgia.” In favor of a spectrum hypothesis, there can be overlap in treatment, as carbamazepine and oxcarbazepine can work in both, although Dr. Cohen recommends lamotrigine and gabapentin first for SUNHA. Of course, lamotrigine and gabapentin can sometimes work in CTN as well, so response to a specific anti-epilepsy drug (AED) does not determine diagnosis either. Dr. Benoliel et al. comment on aberrant vascular loops, commonly seen in CTN, but also on occasion seen in SUNHA and possibly responsive to microvascular decompression. Even pathophysiology may be shared. Drs. Benoliel et al. describe the overlap and differences in prevalence, age of onset and gender predilection, location of symptoms and signs, pain quality and severity, disease and attack duration, cranial autonomic signs (CAS), triggering, refractory periods, sensory deficits, concomitant persistent facial pain (background pain), sleep attacks, pathophysiology, and response to therapy. His meticulous, encyclopedic literature review on each of these clinical considerations should convince Headache Medicine experts that openmindedness and humility may be the best approach in the next patient presenting with either of these disorders. These reviews both merit very careful reading, and I have returned to re-read them numerous times already.