A 51-year-old female with four month history of a facial pain in left maxillary nerve innervated territory was referred to the department of anesthesiology and pain. There were not any initiating factors associated with this pain. She suffered from constant deep aching pain over the left maxillary area. Her pain intensity was 5-7 using visual analogue score (VAS: 0 = "no pain" and 10 = "worst pain imaginable"). There were no abnormalities in her imaging studies including X ray and MRI for head and face and blood laboratory examination such as erythrocyte sedimentation rate and C reactive protein. She was diagnosed with AFP syndrome by a dentist and tramadol 150 mg a day, imipramine 20 mg a day and pregabalin 300 mg a day were given. But these medications did not reduce the pain. Except her pain, physical examination showed no abnormal findings. The pain was increased by cold innocuous stimulation and we performed a thermograhic study on her face. The study revealed that the temperature was significantly lower in the left maxillary area than the right maxillary area (Fig. 1). Therefore, SGB was performed by injection of 6 ml of 1.5% lidocaine at the anterior aspect of the left 6th cervical transverse process. Two minutes after SGB ipsilateral Horner's syndrome developed and twenty minutes after SGB her pain intensity decreased to 1-2 on the VAS. We performed SGB 2-3 times a week. After the 12nd completion of SGB, her pain disappeared and she stopped medications. At 2 months follow-up, she continued to have no pain.

A diagnosis of AFP is made when patients present with symptoms that do not fulfill any criteria available. It has several features such as no objective signs, no obvious explanation of the cause and poor response to treatments. Psychogenic problems such as depression and anxiety were often associated with AFP. It is reported that AFP commonly occurs in middle aged or elderly females [10,11].

SGB is a selective sympathetic block that influences ipsilateral head, neck, and upper extremities. SGB help increase circulation and blood supply to the arm and are used to relieve vasospasm [12]. In addition, it has been used in treating various diseases such as post- herpetic neuralgia, migraine and complex regional pain syndromes [3,4,5]. Sympathetic activity may generate pain under certain pathological conditions. In sympathetically maintained pain cases, the receptors at the primary afferents can change and become sensitive to adrenergic substances such as norepinephrine [13,14]. It was reported that SGB is effective to reduce pain related to temporal arteritis and sympathetic maintained headache and orofacial pain [15,16]. Sympathetic block can improve blood flow by dilating vessels. In addition, sympathetic block may reduce pain by directly blocking afferent nociceptive signal traveling via sympathetic pathways [17]. Chronic stimulation of nociceptive system may lead to a demyelination and axonal dysfunction in addition to an overactivation of central sensory transmission. This could result in atypical chronic pain instead of a typical neuralgia [18]. Recently it was reported that SGB has selective effects in animal and human study. The sedative effects of SGB can be one of therapeutic actions for treating various pain disorders [8,9].

In this case, the pain is increased by cold innocuous stimulation and thermography showed that the temperature on the painful area was significantly decreased. And SGB successfully alleviated the atypical facial pain involving maxillary nerve territories.

In conclusion, SGB can be effectively used to treat AFP. Further research is needed to define its role in managing chronic pain conditions like AFP.