The puzzle of V1 trigeminal neuralgia and SUNCT

Dear Sir,

We read the paper by Di Stefano et al. (1) with great interest. The authors studied the trigger maneuvers, frequency of triggers and location of trigger zones in trigeminal neuralgia. We believe that this subject has not been systematically studied in the past, which has left several unanswered questions regarding TN. The authors’ observation regarding the frequency and location of trigger zones, in our view, will be widely agreed upon by most experts in this field.

One third of their patients had TN in the distribution of the ophthalmic division (V1TN) of the trigeminal nerve. In our experience, and as suggested by the previous studies, this distribution of TN is relatively less common (2). The V1 TN is different from the maxillary and mandibular division of TN, as involvement of the ophthalmic division may produce overt autonomic symptoms like lacrimation, conjunctival congestion, rhinorrhea, and forehead sweating in around 30% of patients (2). These features are also shared by an entity called short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT). SUNCT can have both spontaneous and triggered pain attacks, as with TN. This adds to the confusion between these two entities. Higher frequency and severity of pain attacks, severe autonomic features and poor response to carbamazepine are suggested as useful differentiating features. However, these features are also described with “severe” TN. Another feature that was suggested to differentiate TN and SUNCT is the absence of a refractory period between the subsequent triggered pain attack in SUNCT. However, we described three patients with SUNCT with variable refractory periods between the subsequent triggered attack (3). Recently, several authors have argued that due to the unclear divide between the two entities, TN and SUNCT may be same disorder, but of different severity (4). However, TN is placed among “painful cranial neuropathies and other facial pains” whereas SUNCT is classified as “trigeminal autonomic cephalalgias” in the International classification of headache disorders, third edition (5).

We believe that with so many patients suffering from V1 TN, the authors have the unique opportunity to answer many questions. They can compare the trigger characteristics between V1 TN to those with V2 and V3 TN. We understand that the focus of their study was triggers; nevertheless, we believe that it would be more useful if they report autonomic symptoms (proportion and type) in V1 TN patients, which may help in differentiation of V1 TN from SUNCT. The proportion of V1TN patients showing refractoriness to subsequent triggered attacks among those with and without autonomic features could have helped understanding of the importance of triggers in better characterization of these patients. This could help to some extent to remove the ambiguity regarding the diagnosis of V1 TN.