This pattern occurs when a large, contiguous body area of sweat loss with sharply demarcated borders conforming to sympathetic or somatic dermatomes are present.
Sympathectomy, ganglionopathies and myelopathies produces such pattern. When borders are not well defined and anhidrosis not contiguous, a regional pattern is said to exist. Both postganglionic and preganglionic lesions may produce these distributions. (p.557)