Kingma D W, Feeback D L, Marks W A, Bobele G B, Leech R W, Brumback R A
Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
J Child Neurol. 1991 Oct;6(4):329-34. doi: 10.1177/088307389100600408.
The diagnostic muscle biopsy finding in severe infantile spinal muscular atrophy (Werdnig-Hoffmann disease, SMA type 1) is considered to be large-group atrophy with isolated clusters of hypertrophic type I myofibers. We present a unique case of severe infantile spinal muscular atrophy with selective hypertrophy of type II myofibers. A male infant presented at age 2 months with breathing difficulties and by age 4 months was hypotonic and weak. Electromyography revealed denervation in all extremity muscles, and nerve conduction velocities were normal but with small compound muscle action potentials. Quadriceps muscle biopsy revealed many hypertrophied type II myofibers (myofibers with a mean least diameter of 25.4 microns). In contrast, the largest type I myofibers were 20 microns in least diameter (mean diameter, 14.9 microns), and there was a normal-size population of type II fibers (mean diameter, 15.7 microns). In addition, sheets of atrophic type I and type II fibers averaged 2.0 microns in least diameter. Sural nerve biopsy was normal. Breathing difficulties progressed, with death ensuing at age 5 1/2 months. Autopsy revealed atrophy of ventral spinal roots with normal dorsal roots. There was loss of anterior horn cells, while remnant neurons were reduced in size. No other pathologic changes were identified. This case indicates that in severe infantile spinal muscular atrophy, relative sparing of the motor units with type II myofibers may occur.
严重婴儿型脊髓性肌萎缩症（韦尼克 - 霍夫曼病，1型脊髓性肌萎缩症）的诊断性肌肉活检结果被认为是大群性萎缩伴有孤立的肥厚性I型肌纤维簇。我们报告一例严重婴儿型脊髓性肌萎缩症伴有II型肌纤维选择性肥大的独特病例。一名男婴在2个月大时出现呼吸困难，4个月大时出现肌张力减退和肌无力。肌电图显示所有肢体肌肉均有失神经支配，神经传导速度正常但复合肌肉动作电位较小。股四头肌活检显示许多II型肌纤维肥大（平均最小直径为25.4微米的肌纤维）。相比之下，最大的I型肌纤维最小直径为20微米（平均直径为14.9微米），并且有正常大小的II型纤维群体（平均直径为15.7微米）。此外，萎缩的I型和II型纤维片层平均最小直径为2.0微米。腓肠神经活检正常。呼吸困难进展，患儿在5个半月时死亡。尸检显示腹侧脊髓神经根萎缩而背侧神经根正常。存在前角细胞丧失，而残余神经元体积减小。未发现其他病理变化。该病例表明，在严重婴儿型脊髓性肌萎缩症中，可能会出现具有II型肌纤维的运动单位相对保留的情况。
