Case Presentation: A 71-year-old male with history atrial fibrillation presented with dyspnea and splenomegaly. Patient was admitted for worsening hypoxemia found to have large bilateral pleural effusions. Peripheral smear performed for anemia and splenomegaly notable for monocytosis. Patient had 20 lbs weight loss in two months. Bone marrow biopsy revealed absolute monocytosis, morphologic findings suspicious for MPN/MDS and ultimately diagnosed with CMML. He developed rapidly progressing leg numbness and weakness, leading to flaccid paraplegia, with bilateral positive Babinski signs, neurogenic bladder, and loss of bowel tone. Spinal MRI revealed intramedullary T2 hyperintensity from T5-T6 to T11-T12 with central cord signal predominance. No clear sensory level elicited on exam. Lumbar puncture was unrevealing. CSF and serum were negative for paraneoplastic antibody panel. NMO and MOG antibodies are negative. MYD88 normal. Encephalitis ENC2 panel negative. Patient was initiated on methylprednisolone 1000 mg/d, PLEX, and IVIG. Post-treatment MRI with significantly decreased T2 hyperintense signal abnormality in mid and lower T spine. Physical exam with improvement of plantar and dorsiflexion. Some contraction of quadriceps. EMG showed evidence of moderate length-dependent sensory motor primarily axonal polyneuropathy. Patient was treated with rituximab for maintenance therapy. One-month follow-up MRI showed resolution of spinal lesions, and patient was ambulatory at seven months.
Discussion: The patient’s presentation is most consistent with paraneoplastic transverse myelitis secondary to CMML. CMML was diagnosed using WHO criteria, including absolute monocyte count ≥0.5 × 10⁹/L, monocytes ≥10% of WBCs, and monocytosis ≥3 months. Bone marrow biopsy confirmed absolute monocytosis. Lack of a BCR-ABL1 fusion gene ruled out CML, and rearrangements of PDGFRA, PDGFRB, FGFR1, or PCM1-JAK2 were absent, ruling out myeloid/lymphoid neoplasms with eosinophilia. Blasts < 20% indicated no AML transformation. Dysplasia remains possible if monocytosis persists ≥3 months or if clonal abnormalities are present.Transverse myelitis was supported by physical exam and MRI showing a T-spine hyperintense lesion extending across ≥3 segments. MRI confirmed LETM and ruled out infarct, abscess, and compression. LETM is most common in NMOSD, MOGAD, and MS, so the workup included complete spinal and cranial MRI, lumbar puncture, and serologic testing (APL, RF, ANA, anti-dsDNA, AQP4-IgG). Elevated CSF cell count triggered infectious evaluation, all of which was negative (PCR testing, TB, HIV, syphilis, Lyme). NMO and MOG antibodies were negative, ruling out autoimmune causes. Thus, findings supported paraneoplastic CMML-associated LETM.Paraneoplastic LETM is rare, and CMML-associated LETM has never been reported, making this the first. Treatment responses vary, but our patient improved with physical therapy, PLEX, and steroids. A myelodysplastic syndrome remains possible with persistent cytopenia or dysplasia. Mechanism may differ from LETM in solid tumors. Dysplastic monocytes in CMML may create a pro-inflammatory environment decreasing immune tolerance and promoting CNS-directed autoantibodies. Prognosis varies; mortality is ~10% at 3 years, with 17% having EDSS ≥7 and 83% ambulatory.
Conclusions: Though rare, it is important to note that our case of CMML-associate LETM responded with physical therapy, PLEX, steroids, and Rituximab allowing the patient to have slow return of leg function.