Rigid spine syndrome (RSS) is a group of childhood-onset muscle disorders characterized by marked limitation of flexion of the spine. Various cardiac changes have been documented in case reports. This study reports on a cardiac evaluation of nine patients with the “vacuolar variant” of RSS. Noninvasive cardiac evaluation entailed creatine kinase levels, full-inspiration chest roentgenograms, standard 12-lead ECG, and 24-h ambulatory ECG recording, as well as M-mode and two-dimensional echocardiography with Doppler study. Heart auscultation was abnormal in five patients. Creatine kinase MB fraction was normal in all patients. Chest roentgenogram showed scoliosis (five of nine), kyphosis (one of nine), severe anterior-posterior flattening of the chest cavity (two of nine), elevated hemidiaphragm (one of nine), caved-in appearance of upper lobes (two of nine), and symmetry of lung volumes (one of nine). Twelve-lead ECG abnormalities indicated right-sided heart disease (three of nine). Echocardiogram showed mitral valve prolapse (five of nine) with regurgitation (three of five) and evidence of pulmonary hypertension (three of nine). Ambulatory ECG recorded paroxysmal tachyarrhythmias in hypoxic or hypercapnic patients (three of nine). There was no correlation between any cardiac abnormalities and patient weakness. Mitral prolapse/regurgitation may have a developmental association with this congenital myopathy. Findings of cor pulmonale were due to the restrictive chest wall defect and respiratory muscle weakness. Paroxysmal tachyarrhythmias were due to hypoxia or hypercapnia. There was no evidence of a primary cardiomyopathy.
Rigid spine syndrome (RSS) is a rare childhood-onset muscle disorder characterized by marked limitation of flexion of the spine; progressive scoliosis; contracture of limb joints, especially the elbows; mild and nonprogressive, proximal weakness; moderately elevated muscle enzymes; a “myopathic” electromyogram pattern in spinal muscles; and histologic features of a nonspecific myopathy with marked fibrosis [5, 6]. Doubts have been expressed whether RSS is a single nosologic entity, as the hereditary patterns, degree and distribution of weakness, cardiac involvement, and muscle histology vary considerably in reported cases [2, 13, 19].
Various cardiac changes have been reported, including complete heart block, interventricular septum hypertrophy, and enlargement of the left atrium and ventricle [2, 17, 18]. It appears that cardiomyopathy occurs concomitantly with the skeletal manifestations in some patients with this syndrome.
We described the phenotype and muscle histopathology findings of nine patients with RSS. The salient pathology features were autophagic vacuoles, vacuoles containing capillaries, muscle spindle swelling, and type 1 muscle fiber predominance. The term “vacuolar variant” of RSS was proposed . The respiratory manifestations of these patients included severe restrictive chest wall defect and limited mobility of the spine associated with clinically significant respiratory muscle weakness . In some patients the slowly progressive respiratory muscle disease led to hypercapnic ventilatory failure. During this study clinical features of cor pulmonale without right-sided cardiac failure were detected in three patients. Therefore, a detailed noninvasive cardiac evaluation was performed as part of a complete systems review. There was no clinical indication to perform any invasive testing.