The back can have a wide distribution in shingles; and according to a study, is not relable at determining nerve level, as is the front distribution. I will inject dorsal nerve roots in order to shut the back distribution off; often I have to inject several levels.
Feasibility of locating the infected spinal nerve roots by skin lesion in herpes zoster
Huang, L et al
Pain Clinic Journal October 2012 8(5) 328-330 abstract here
- nerve block proved accuracy of level in 94.8% of anterior areas but only 7.7% of posterior areas
Comment – for cervical and thoracic, the dorsal nerve root comes to skin close to spinous process and a little skin local nerve the spinous process should do. For the lumbar, I angle in from the lateral paraspinous border maybe 40 degrees inward and inject local at depth of 1 inch. Be prepared to do several levels; though anteiorly, several levels are sometimes necessary as well.