Neurolymphomatosis Caused by Nasal-type Extranodal Natural Killer/T-cell Lymphoma

Correspondence To the Editor: Neurolymphomatosis (NL) is a clinical disorder that presents with peripheral neuropathy due to lymphomatous infiltration of the nerves. NL is generally associated with B-cell lymphomas, and T‑cell lymphoma is extremely rare. Nasal type extranodal natural killer (NK)/T‑cell lymphoma (ENKL) is a rare lymphoma associated with Epstein‑Barr virus (EBV), which is more common in East Asia than in the West. [1] Central nervous system (CNS) lesions are occasionally observed as sites of ENKL involvement, and extranodal involvement often leads to an unfavorable prognosis. Here, a rare case of NL associated with ENKL that mainly presented as progressive multiplex painful mononeuropathy with multiple white matter lesions is reported. A 26‑year‑old woman referred to our hospital after presenting asymmetrical numbness, pain, and weakness of bilateral legs with an intermittent fever for 3 months. The patient had experienced significant weight loss, but her prior medical history was not significant. Physical examination revealed patchy erythema with blisters on her distal arms. Neurological examination revealed paralgesia in the left planta, distal arm, outer calf, and inside of the right calf. The left Achilles tendon reflexes decreased. The left upper limb muscle strength was 2/6 distally and 3/6 proximally. Positive Babinski's sign was observed on the left side. The patient was considered to have possible CNS involvement, multiplex mononeuropathy, and skin lesions. The laboratory findings included slight anemia (hemoglobin 108 g/L; normal: 115–150 g/L), thrombocytopenia (platelet [PLT]: 100 × 10 9 /L; normal: 125–350 × 10 9 /L), an elevated lactate dehydrogenase level (lactate dehydrogenase: 276 U/L; normal: 125–225 U/L), and an extremely elevated ferritin level (>572 μg/L; normal: 10–140 μg/L). The cerebrospinal fluid was not remarkable. Electromyography revealed diminished or no compound muscle action potential and sensory nerve action potential amplitude in the left median and ulnar nerves and the right tibialis anterior nerves, indicating multiplex mononeuropathy with axonal damage. Two courses of high‑dose dexamethasone therapy resulted in transient improvement of the patient's temperature and neurological symptoms, while the thrombocytopenia worsened (PLT: 51 × 10 9 /L). Bone marrow puncture revealed some atypical lymphocytes, but flow cytometry was negative. Magnetic resonance imaging of the brain revealed multiple white matter lesions with no enhancement [Figure 1a and 1b]. An 18 F-fluoro-2-deoxyglucose positron emission tomography (FDG‑PET) scan demonstrated extensive involvement of the left brachial plexus nerve, right tibial nerve, left median nerve, left ulnar nerve, CNS, muscle, nasopharynx, and skin [Figure 1c]. Finally, skin …