Contributed by Bernardo-Cofiño J, MD1, Gómez-Illán R, MD2, Nicolás C, MD3, Astudillo A, MD, PhD4,5 and Fernandez-Vega I, MD PhD4,5
1Internal Medicine Department and 2Radiology Department at Centro Médico de Asturias, Oviedo, Spain. 3Hematology Department at Hospital Universitario Central de Asturias
4Pathology Department (Neuropathology Division) and 5Biobank of Principality of Asturias at Hospital Universitario Central de Asturias, Oviedo, Spain.
We present a 66-year-old woman with a previous medical history of probable polyarteritis nodosa (PAN) diagnosed by our medical team six months ago, performing a complete laboratory workout including hematological, neurophysiological, biochemical (checking blood and cerebrospinal fluid), microbiological and radiological tests. A subacute demyelinating polyneuropathy was noticed at that time. Eventually, she received cyclophosphamide in combination with high dose corticosteroid therapy with a significant clinical improvement. Almost six months thereafter, she was admitted to Internal Medicine Department because of a casual midnight fall suffering cranial contusion and transient fever. Physical examination pointed out mild confusion, one facial bruising over her right malar region and remarkable proximal weaknesses to grade 3/5 in the upper limbs and 2/5 in the lower limbs, leaving her unable to walk but preserving sensory responses. According to clinical evolution and her medical history, steroid myopathy was considered as a potential cause of her muscle weakness. However, during her hospitalization she developed acute respiratory failure, treated with corticosteroid bolus and intravenous immunoglobulins, recovering from her respiratory failure and her muscular weakness. CK levels were always within normal limits. In this light, a possible vasculitic myopathy versus amyopathic myositis was considered. MRI performed in both thighs showed a significant muscular edema with perifascial, muscle and subcutaneous hyperintensities (Figures 1a and 1b). Then, the leading diagnostic consideration was inflammatory myopathy. Autoimmune antibodies were tested such as anti-Mi2, KU, Pm-Scl100, Jo-1, SRP, PL-7, PL12, EJ, OJ, Ro, NMDA, Mus-ck and acetylcholine and did not show abnormal results. Then, a muscle biopsy was considered and it was performed on the left thigh.
On H&E the biopsied specimen did not show architectural alterations (Figures 1c, 1d). At the structural level, muscle fibers appeared normal. However, there were almost 25% type II round atrophy muscle fibers without type grouping. Additionally, scattered angular atrophic esterase-positive muscle fibers were noted as indicative of acute denervation atrophy. (Figures 1c, 1d): black arrows pointing out perimysial blood vessels; white arrows pointing out endomysial blood vessels; black asterisk pointing out round atrophy muscle fibers; white asterisk pointing out angular atrophy muscle fibers). Furthermore, some perimysial and endomysial vessels contained a neoplastic cells accumulation of abundant atypical lymphocytes (Figures 1e, 1f). Neoplastic cells were not found to infiltrate the endomysium and/or perimysium. Neither fiber necrosis nor features of fiber regeneration were noted. Immunohistochemical staining showed cells were positive for CD20 (Figure 1g), CD79a, Pax5, BCL2 (Figure 1h), BCL6 and MUM-1(Figure 1i); and negative for CD3 and CD10. The mean Ki-67 proliferation rate was 90% (Figure 1j), indicating the tumor was in an active growing status. What is your diagnosis?