Lateral Cutaneous Nerve Entrapment Syndrome (LACNES): A previously unrecognized cause of intractable flank pain.

BACKGROUND AND AIMS: Chronic abdominal pain may occasionally be due to terminal endings of intercostal nerves (ACNES, abdominal cutaneous nerve entrapment syndrome) that are entrapped in the abdominal wall. Spontaneous neuropathic flank pain may also be caused by involvement of branches of these intercostal nerves. Aim is to describe a series of patients with flank pain due to nerve entrapment and to increase awareness for an unknown condition coined Lateral Cutaneous Nerve Entrapment Syndrome (LACNES).

METHODS: Patients possibly having LACNES (constant area of flank tenderness, small point of maximal pain with neuropathic characteristics, locoregional altered skin sensation) presenting between January 2007 and May 2016 received a diagnostic 5-10mL 1% lidocaine injection. Pain levels were recorded using a numerical rating scale (0, no pain to 10, worst possible). A >50% pain reduction was defined as success. Long term effect of injections and alternative therapies were determined using a satisfaction scale (1, very satisfied, no pain - 5, pain worse).

RESULTS: 30 patients (21 women, median age 52, range 13-78) were diagnosed with LACNES. Pain following one injection dropped from 6.9±1.4 to 2.4±1.9 (mean, p<0.001) leading to an 83% immediate success rate. Repeated injection therapy was successful in 16 (pain free n=7, pain acceptable, n=9; median 42 months follow-up). The remaining 14 patients received (minimally invasive) surgery (n=5) or other treatments (medication, manual therapy or pulsed radiofrequency, n=9). Overall treatment satisfaction (scale 1 or 2) was attained in 79%.

CONCLUSIONS AND IMPLICATIONS: LACNES should be considered in patients with chronic flank pain. Injection therapy is long term effective in more than half of the population.