Case Report Heralding Extramedullary Blast Crisis: Horner’s Syndrome with Brachial Plexopathy in a Patient with Chronic Myelogenous Leukemia Sajish Jacob 1 and Sadanand I. Patil 2 1 Memphis Neurology, 1407 Union Avenue, No. 1400, Memphis, TN 38014, USA 2 Baptist Cancer Center, 6029 Walnut Grove Rd, No. 300, Memphis, TN 38120, USA Correspondence should be addressed to Sajish Jacob; sjacob@memphisneurology.com Received 18 September 2016; Accepted 1 December 2016 Academic Editor: Tomas R. Chauncey Copyright © 2016 S. Jacob and S. I. Patil. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chronic myelogenous leukemia (CML) blast crisis is an ominous clinical event that is challenging to treat. Tis can develop at extramedullary sites rarely and is defned as the infltration of blasts outside the bone marrow irrespective of proliferation of blasts within the bone marrow. We aim to report an unusual clinical presentation characterized by Horner’s syndrome, ipsilateral arm weakness, and cervical lymphadenopathy as the frst signs of extramedullary blast crisis in a CML patient. To the best of our knowledge, the extramedullary locations involving the brachial plexus along with cervicothoracic paraspinal chloroma have not been previously reported in the literature. 1. Introduction Chronic myelogenous leukemia (CML) is classifed as a myeloproliferative neoplasm which usually progresses from a relatively indolent disease to a more aggressive disorder, during which time disease control is harder to achieve [1]. In virtually all patients, the disease culminates into an acute leukemic phase, especially if untreated, termed “blast crisis.” Blast crisis of CML is an ominous clinical event that can further be divided based on the site of origin: medullary or extramedullary [2]. Extramedullary blast crisis is extremely rare and is defned as the development of extramedullary blasts infltration irrespective of the proliferation of blasts in the bone marrow [3]. We report an unusual clinical presentation heralding blast crisis transformation in a CML patient, characterized by cervical lymphadenopathy, cervi- cothoracic paraspinal chloroma with leukemic infltration of the brachial plexus causing lef Horner’s syndrome, and ipsilateral symptomatic arm involvement. 2. Case Presentation A 36-year-old African American male diagnosed with Phil- adelphia chromosome positive CML two years ago presented to the emergency room for the second time with a history of a one-month progressively worsening weakness involving his lef upper extremity, along with numbness and severe pain. His symptoms during the previous hospital evaluation were attributed to musculoskeletal causes afer stroke was ruled out. Although he was unsure, he was reported by family members to have developed some facial asymmetry during this time. He had been noncompliant with his treatment with dasatinib, being irregular and casual in his approach to prescribed medication intake, and his primary oncologist was concerned with CML progression at an accelerated phase afer having undergone a bone marrow biopsy. He was meanwhile awaiting the results of a recent cervical lymph node biopsy. On neurological examination the patient was noticed to have lef-sided ptosis, miosis, enophthalmos (Figure 1), Hindawi Publishing Corporation Case Reports in Medicine Volume 2016, Article ID 3015947, 5 pages http://dx.doi.org/10.1155/2016/3015947