ORIGINAL ARTICLE Myofascial Trigger Points in Early Life Mu-Jung Kao, MD, Ting-I Han, MD, Ta-Shen Kuan, MD, MS, Yueh-Ling Hsieh, PhD, PT, Bai-Horng Su, MD, Chang-Zern Hong, MD or ABSTRACT. Kao M-J, Han T-I, Kuan T-S, Hsieh Y-L, Su B-H, Hong C-Z. Myofascial trigger points in early life. Arch Phys Med Rehabil 2007;88:251-4. Objective: To determine whether latent myofascial trigger points (MTPs) can be identified in healthy infants and in healthy adult subjects. Design: Blind comparison. Setting: Ambulatory. Participants: A convenience sample of 60 healthy adults and 60 infants (age range, 0-12mo). Interventions: Not applicable. Main Outcome Measures: An algometer was used to mea- sure the pressure pain threshold (PPT) on 3 different sites, including a midpoint (assumed to be the MTP site) in the brachioradialis muscle. Results: The mean PPT values at the MTP site were signif- icantly lower than the other sites in the adult muscles. How- ever, no significant differences in PPT values among these 3 sites were found in the infants. Taut bands were found in all the adult muscles but none in the infants. Conclusions: In the adult subjects, the midpoint of brachi- oradialis muscle was significantly more irritable than other sites and the midpoint was probably a latent MTP. However, in the infants younger than 1 year old, such a phenomenon could not be observed in this study. It is very likely that the latent MTPs might not exist in early life, but develop in later life. Key Words: Infant; Muscle; Pain; Rehabilitation; Trigger points, myofascial. © 2007 by the American Congress of Rehabilitation Medi- cine and the American Academy of Physical Medicine and Rehabilitation A CCORDING TO THE classical definition, a myofascial trigger point (MTP) is a hypersensitive spot in a taut band of skeletal muscle fibers. 1 Latent MTPs are tender to palpation but do not cause spontaneous clinical pain. Active MTPs typically cause spontaneous painful symptoms referred to a site distant from the MTP and are painful to palpation. Normal adults usually have latent MTPs in the clinically “normal” (nonpainful) muscles. It has been hypothesized that latent MTPs may become active in response to a stimulation from a lesion in a site other than the MTP itself, reflexively via the spinal cord, as a consequence of central sensitization. 1-4 In other words, an active MTP is probably an acquired phenom- enon, although it is still unknown whether a latent MTP is acquired or congenital. The pathophysiology of the MTP has now become better understood, based on recent electrophysiologic studies on both human and animal subjects. 2-15 It has been hypothesized that there are multiple sensitive MTP loci in an MTP region. 5 Histologic study suggested that these sensitive loci might be sensitized nociceptors. 16 An MTP is usually identified in the endplate zone (usually, the middle portion of the muscle fi- bers). 14,15 Based on electrophysiologic studies, in an MTP region, a sensitive locus is usually found in the vicinity of an endplate. 14,15 The endplate near the sensitive locus of an MTP has been considered as a dysfunctional endplate with excessive acetylcholine leakage, based on the electrophysiologic stud- ies. 12,14,15 The endplate noise, instead of miniature endplate potentials, can be recorded frequently in an MTP region, be- cause MTPs are usually found in the endplate zone containing some dysfunctional endplates. The result of excessive secretion of acetylcholine, the “contracture knot,” has been demonstrated in a histological study in dog. 1,17 It appears that the pathogen- esis of MTP may involve both sensory and motor components, the nociceptor and the motor unit. However, the pathogenesis of the formation of an MTP is still unclear. Based on clinical observation and informal studies, Hong 3,4,18 has claimed that newborn babies and infants may have no MTPs, and, as they grow up, latent MTPs may develop gradually. However, because we have found no support for this view in the literature, we have designed this study to investi- gate the occurrence of latent MTP in early life. The hypothesis is that latent MTPs cannot be found in early life, but may develop gradually when the newborns grow up. METHODS General Design For each infant or adult subject, we measured the pressure pain threshold (PPT) with a pressure algometer at 3 different sites (the midpoint was assumed to be the site of latent MTP) of the brachioradialis muscle to see if the MTP site was more irritable (with lower PPT) than the other sites. Our institutional review board has reviewed and approved this study. Participants We recruited 60 adults and 60 infants aged less than 1 year for this study. The subjects or their legal guardians signed the informed consent forms that were approved by the institutional review board of a university hospital. The mean age of the subjects and the age distribution of the infants are shown in table 1 and figure 1, respectively. The exclusion criteria included any acute or serious illness, any trauma to the upper limb, any deformity in the upper limb, or any signs of emotional instability or evidence of poor cooperation. From the Department of Physical Medicine & Rehabilitation, Taipei City Hospital, Taipei, Taiwan (Kao); Department of Rehabilitation Medicine, College of Medicine, China Medical University, Taichung, Taiwan (Kao); Departments of Rehabilitation Medicine (Han) and Pediatrics (Su), China Medical University Hospital, Taichung, Taiwan; Department of Physical Medicine & Rehabilitation, College of Medicine, National Cheng-Kung University, Tainan, Taiwan (Kuan, Hong); and Department of Physical Therapy, Hungkuang University, Taichung, Taiwan (Hsieh, Hong). Supported by the National Science Council (Taiwan) (grant no. NSC93-2314-B- 241-002). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s)is/are associated. Reprint requests to Chang-Zern Hong, MD, Dept of Physical Therapy, Hung- Kuang University, 34, Chung-Chie Rd, Sha-Lu, Taichung 433, Taiwan, e-mail: czhong@cox.net. 0003-9993/07/8802-11107$32.00/0 doi:10.1016/j.apmr.2006.11.004 251 Arch Phys Med Rehabil Vol 88, February 2007