Other Neuromuscular Conditions and Spina Bifida
Kenneth J. Noonan, MD, MHCDS
Robert M. Kay, MD1
Tips for Recognizing Neuromuscular Conditions
The array of diagnosable neuromuscular conditions presenting in children is interesting but sometimes intimidating. Most of this information is generally toward the periphery of most orthopaedic surgeons’ knowledge. Stay out of trouble by knowing a few common threads in these conditions that can help you identify a child with a potential neuromuscular condition. Also, don’t be afraid to ask parents what syndrome their child has and ask them to enlighten you. Parents like doctors who are not know-it-alls but are willing to learn from them.
THE GURU SAYS…
It’s good to get into the habit of asking about milestones when seeing new patients. A good rule of thumb is that if a child is not hitting his milestones by 1.5 times the typical age for such milestones, then he is outside the normal range. As such, while the mean time for sitting, standing, and walking are 6, 8, and 12 months, respectively, children are outside the “normal” range if not hitting these milestones by 9, 12, and 18 months and should be worked up for their developmental delay.
A common scenario occurs when parents bring a child to an orthopaedic surgeon because the child walks funny, falls down, wants to be carried when walking far, or some other seemingly innocuous complaint. Ninety-nine percent of the time, it is age appropriate, but this chapter may help with the other 1%. Delay in diagnosis can have serious implications. In addition to delaying treatment of the child’s condition, it can also result in transmitting the same disease to younger siblings; as an example, before Duchenne muscular dystrophy (DMD) is diagnosed, 20% of families already have conceived a second child. Do not hesitate to examine the parents (subtle cavovarus feet, café au lait spots, etc.) and ask for a family history. Many parents have unrecognized subtle forms of the same disease as their child. This aids in diagnosis of the child.
THE GURU SAYS…
▶ Hand dominance should not occur before 1 year of age. If a child younger than 1 year old is hand dominant, there is almost always an underlying neuromuscular condition.
▶ Red Flags That a Child May Have a Neuromuscular Disorder
▶ “Floppiness” as an infant, inability to sit independently
▶ Delayed crawling
▶ Delayed walking (consider up to 18 months for achievement of independent ambulation “normal”—one must often clarify to the parents that this means the child walks without the child holding on to anything)
▶ Complains of tiring easily when walking
▶ Tripping or falling if new-onset or worsening gait
▶ Difficulty navigating stairs
▶ No complaints of pain
▶ Hypotonia or hypertonia (though this seems to be overdiagnosed these days)
▶ Changing or progressive deformity of feet (Fig. 17-1)
▶ Involvement is symmetrical (except for hemiplegia; if asymmetrical, think spine pathology)
THE GURU SAYS…
There are many important nonorthopaedic conditions associated with many of the neuromuscular conditions, which may have more immediate implications than the orthopaedic issues. For instance, children with trisomy 21 (Down syndrome) often have congenital cardiac defects, and thyroid disease is also common. Children with muscular dystrophies often have progressive cardiac dysfunction and may have life-threatening cardiac conduction defects.
General Principles of Treatment
Do not become focused on one body part as many neuromuscular conditions have multiple orthopaedic implications. For example, a child with Charcot-Marie-Tooth (CMT) disease may present to you with a foot deformity, but do not forget there is an increased risk of scoliosis1 and hip dysplasia.2,3 This raises an important point even for pediatric orthopaedic surgeons who feel comfortable seeing children with neuromuscular conditions. Each condition has its own unique pitfalls, and it is probably worthwhile to quickly review literature on a child’s condition prior to instituting treatment. For example, children with various muscular dystrophies have widely variable prognoses. Know the natural history and expected function of the condition prior to planning surgery as many of these children may never be expected to walk, or even live very long, which may influence whether surgery is indicated. If a muscle biopsy is required, biopsy the weak muscle—i.e., the deltoid, for shoulder girdle weakness.
THE GURU SAYS…
As the field of medicine continues to advance rapidly, the natural history of neuromuscular diseases can be dramatically changed by new treatments. Spinal muscular atrophy (SMA) is a recent example of a disease whose prognosis has been dramatically improved by medical advances, which has also changed the orthopaedic treatment paradigm in patients with SMA.
THE GURU SAYS…
You should check with the pathologist before doing a muscle biopsy to confirm what type of specimen she wants. Placing muscle clamps on the muscle before taking the biopsy, and leaving them in place, is often preferred by pathologists since it allows the muscle to be at its resting length and maintain its structural properties and architecture while it is examined microscopically.
Latex Allergy: Not Just in Spina Bifida
Many children with a variety of neuromuscular disorders (including cerebral palsy) have had multiple exposures to latex (ventriculoperitoneal shunt, catheterization, pre-vious surgeries, etc.) and may be considered at risk for latex allergy and intraoperative anaphylaxis.4
THE GURU SAYS…
It’s a good idea to always have a latex-free environment in both the office and operating room settings to avoid any potential latex reactions.
Children with neuromuscular disease and decreased ambulation are at an increased risk for osteopenic fractures. In an insensate area, fractures are often not appreciated at the time of injury and present late as a swollen, red, and warm limb that is often mistaken for infection by the inexperienced. To make things even more confusing, the child may present with a fever and abnormal laboratory studies. This scenario unfortunately occurs in children who have severe communication challenges (Figs. 17-2, 17-3 and 17-4).
Fracture care in these children is quite different than in otherwise normal, active children. First, mobilization should begin as early as possible. If a child with progressive weakness and increasing difficulty in walking (e.g., 11-year-old boy with Duchenne muscular dystrophy) is in a long leg cast that prevents walking for 6 weeks, the child may lose so much muscle strength that he never walks independently again. You do not want to contribute to that. Second, immobilize for as little a time period as possible. Immobilization leads to localized osteopenia. These children already have some degree of osteopenia to begin with; following immobilization, fractures at other areas in the limb are quite possible. One of the editors (D.L.S.) assumed care of a spina bifida patient who spent 11 months in lower extremity casts for multiple fractures at different locations. Third, these children often have abnormal sensation; soft-tissue problems from cast sores are more likely to occur, and less likely to be recognized, than in the general population.
Figure 17-2 Radiograph of a femur of a nonambulator with cerebral palsy who has sustained multiple femur fractures. The clinical and radiographic appearance of this fracture may be confused with infection.
We have found less-rigid immobilization is a useful technique for fracture care in nonambulatory children with neuromuscular conditions. This can be accomplished with semirigid fiberglass and/or significant padding, such as polyurethane foam. This decreases osteopenia secondary to immobilization, lessens the chance of a secondary fracture at the edge of a rigid cast, and decreases skin problems from poorly sensate soft tissues rubbing against the edge of a hard cast. The good news in this situation is that there’s often rapid and overwhelming callus formation and the child’s demands usually do not require anatomic reduction.
THE GURU SAYS…
Internal fixation may sometimes be considered in children with pathologic fractures due to osteopenia, in order to minimize or eliminate the need for limb immobilization, especially in the setting of severe contractures.
Pearls to Help Diagnosis Other Disease-Specific Conditions
If there is no weight bearing on the upper extremities in the prone position and no head/neck extension by 3 months, think cerebral palsy.
For new-onset lower extremity weakness and falling, think familial diplegia (also called hereditary spastic paraparesis; HSP).
In a child with unilateral cavovarus feet, order a spine MRI scan for spinal dysraphism.
In a child with bilateral cavovarus feet, look at the hands; if there is intrinsic muscle weakness (Fig. 17-5), think hereditary sensory motor neuropathy (CMT). Look at the parent’s feet, if they have same foot deformity…bingo.
If the child shakes your hand, then can’t relax the grip, think myotonic dystrophy.
If the primary complaint is an abnormality in gait, think Friedreich’s ataxia.
Tongue fasciculations = spinal muscular atrophy.
Dermatomyositis: acute onset of weakness and a malar rash.
Figure 17-5 This young man with severe Charcot-Marie-Tooth disease has bilateral cavovarus feet (A) with clawing of his fingers (B). (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)
THE GURU SAYS…
More tips for diagnosis:
HSP can be difficult to differentiate from CP. Some potential helpful indicators include normal milestones at an early age, significant progression of the spasticity, lack of any upper extremity involvement, normal cognition, and—at times—other affected family members.
Most children presenting to the orthopaedist’s office with cavus (or cavovarus) foot deformity have one of the hereditary motor sensory neuropathies (HMSNs), most commonly CMT. There can be significant difference in the severity of the deformity in the two feet in CMT.
Although the great bulk of foot deformities in CMT have a varus component, valgus deformities may also be seen in CMT (particularly in CMT type 2).
Duchenne Muscular Dystrophy
Duchenne is the most common of the muscular dystrophies, and many other types of muscular dystrophy are less severe. The level of creatine phosphokinase (CPK) may be 20 to 200 times normal in children with DMD but can be elevated for patients with other forms of muscular dystrophy as well as many other types of muscle disease. The CPK may be elevated by birth in normal children, but should return to normal quickly. DMD is not that rare, occurring in 1 in 3500 births, so there is a good chance most orthopaedic surgeons will encounter a new patient at some point in their career. While DMD is X-linked and thus occurs only in boys, it can occur in a child with Turner syndrome (XO), and other forms of muscular dystrophies can occur in girls. Rarely, girls can prevent with a DMD phenotype in the setting of the Lyon hypothesis, in which there is inactivation of one of the two X chromosomes. Mental retardation may be present; just because a boy has mental retardation doesn’t mean he doesn’t have muscular dystrophy. Perhaps the greatest way to stay out of trouble in DMD is to make it a practice to do Gower’s test on all 3- to 6-year-old boys with gait abnormalities other than torsion (see Fig. 2-1 in Chapter 2).
THE GURU SAYS…
Dystrophin abnormalities in the brain often lead to cognitive delays and behavioral problems in boys with DMD.
Clues That a 3-6-Year-Old Boy May Have Duchenne Muscular Dystrophy
Normal birth history
Progressively worsening gait and function, new-onset toe walking
Waddling gait secondary to weak hip abductors
Hyperlordosis and anterior pelvic tilt secondary to weak hip extensors
Hyperextension of knee during standing phase
Partially in reaction to ankle equinus
Partially to augment weak quadriceps
Pseudohypertrophy of calves—on palpation a hard, “rubbery” feeling (Fig. 17-6)