Clinical Reasoning: A 23-year-old woman with paresthesias and weakness

A 23-year-old woman presented with a 6-month history of progressive left hand weakness associated with left ulnar distribution numbness and paresthesias. At the onset of these symptoms, she recalled shooting pain up and down the medial left forearm. She denied any neck pain. The patient had been diagnosed with acute myeloid leukemia (AML) type 5a and appendicitis 9 months previously. At that time lumbar puncture and brain and spine MRI were negative for CNS involvement. A right Hickman catheter was placed. She was treated with cytarabine and idarubicin and was thought to be in complete remission after repeated bone marrow biopsies showed no blasts. No intrathecal chemotherapy was given. The appendicitis was treated for 1 month with moxifloxacin prior to an elective appendectomy. Bone marrow examination and peripheral blood smear were normal at the time of neurologic presentation. Questions for consideration: The evaluation of a patient with hand weakness, numbness, and paraesthesias would start with localizing the lesion. A lesion in the CNS, involving the contralateral precentral gyrus and anterior aspect of the postcentral gyrus,1 is highly unlikely, especially with the shooting pain up and down the medial left forearm. In the peripheral nervous system, radiculopathy, plexopathy, or a nerve lesion could be responsible for combined motor and sensory impairment in the hand. Minor repetitive trauma can cause nerve damage, resulting in carpal tunnel syndrome or ulnar neuropathy at the elbow. The radial, ulnar, or median nerve could have been damaged during the patient's recent surgery. Other causes of isolated neuropathy in this patient include a mononeuritis multiplex caused by blast cell infiltration of the left ulnar nerve. The brachial plexus may …