蔡豐州站長的特殊案例: 患者先天左腿比右腿粗2公分. 經過單側小腿神經整形後, 左腿圍縮小1.5公分, 成為34.5公分, 與右腿接近不少(如右圖).
論文題目: Unilateral Calf Hypertrophy Seen in Lumbosacral Stenosis
論文作者: Swartz, Karin R.; Fee, Dominic B.; Trost, Gregory R.; Waclawik, Andrew J.
論文出處: Spine 406; 27, 2002
Pathologic muscle hypertrophy is most commonly associated with myopathic disorders. However, it can rarely occur in neurogenic disorders. Interestingly, for the most part neurogenic muscle hypertrophy involves the calves but has been described in other muscles as well. When it occurs bilaterally, it is usually the result of a polyneuropathy or anterior horn cell disease and is frequently associated with myokymia or neuromyotonia on EMG. When it occurs unilaterally, it is usually the result of an S1 radiculopathy but has been reported with L5 radiculopathy, polyneuropathy, and poliomyelitis. In cases with unilateral hypertrophied muscles, EMG frequently demonstrates complex repetitive discharges, rather than myokymia or neuromyotonia.
Pathophysiology in neurogenic muscle hypertrophy is uncertain but has been discussed in the literature. When muscle biopsies are performed on the affected muscles, the findings vary but for the most part indicate hypertrophy of both Type 1 and Type 2 fibers, usually concomitantly but occasionally in isolation, as well as angulated, atrophic fibers and fiber-type grouping indicating denervation and reinnervation. There are two major theories regarding the development of neurogenic muscle hypertrophy. The first presents chronic muscle stimulation by complex repetitive discharges, myokymia, or neuromyotonia as the cause of hypertrophy; however, not all cases of neurogenic muscular hypertrophy indicate one of these electrophysiologic findings. The second proposed theory suggests that an increase in the workload imposed on the remaining, innervated muscle fibers is the cause. It is thought that Type 2 muscle fiber hypertrophy is the result of increased workload on the remaining nonatrophic Type 2 fibers. Type 1 hypertrophy is considered secondary to the phenomenon of stretch-induced Type 1 fiber hypertrophy in which Type 1 fibers increase in size because of increased stretch applied to them. However, work-induced hypertrophy does not explain why enlarged muscles are weak, and stretch-induced hypertrophy is seen experimentally but has not been shown to occur in humans.
There has been little discussion in the literature as to why this occurs predominately in the distal S1 distribution. It has been hypothesized that this is because the S1 root innervates both flexor and extensor muscle groups that oppose each other. The evidence for an intrinsic predisposition in the S1 nerve root and/or distribution is strong, given that the majority of reported cases of unilateral neurogenic hypertrophy are the result of isolated S1 radiculopathy. These reports indicate S1 nerve root compression by L5–S1 disc disease or foraminal stenosis as well as evidence of isolated S1 radiculopathy on EMG analysis. This report adds additional evidence to the hypothesis that there is an intrinsic predisposition in the S1 root or its distribution that facilitates neurogenic hypertrophy. Our patient had bilateral L5 radiculopathies and right S1 radiculopathy but only had hypertrophy in the distal right S1 distribution. The radiculopathies had a common etiology, lumbosacral stenosis, but only the radicular distribution had muscle hypertrophy.
This patient was thought to have muscle hypertrophy resulting from a neurogenic cause, specifically radiculopathy. Other causes of muscle enlargement were not thought to be present. These include muscle disorders, such as muscular dystrophies, acid maltase deficiency, hypothyroidism, and inflammatory myopathies as well as tendon rupture and muscle infiltration resulting from neoplasm, amyloid, sarcoid, or parasites. A myopathic etiology was not thought to be present because of the focal and unilateral nature of the hypertrophy and lack of myopathic changes on EMG analysis. Myopathic hypertrophy is bilateral and usually diffuse. Physical examination did not suggest tendon rupture. The patient’s history was not suggestive of amyloid, sarcoid, parasites, or neoplasm. The patient’s mildly elevated CK level does not differentiate between a myopathic or neurogenic etiology for the hypertrophy. Some muscular dystrophies have normal or minimally elevated CK levels, and slight CK elevations, up to 5 times normal, are frequent in neurogenic conditions. Other cases of neurogenic muscle hypertrophy have also had slightly increased CK levels. Neurogenic causes for calf hypertrophy, such as anterior horn cell disease, plexopathy, sciatic nerve injury, or polyneuropathy, were not supported by physical examination or EMG analysis. Therefore, a diagnosis of neurogenic calf hypertrophy secondary to S1 radiculopathy was made and supported by the MRI and needle EMG findings. Although there was not S1–S2 foraminal stenosis, the S1 nerve root was considered damaged because of the canal stenosis. Furthermore, after decompressive laminectomy, the patient had resolution of his painful sensory symptomatology and progressive improvement in strength and endurance.
The classic presentation of progressive muscular enlargement associated with some degree of weakness corresponding with dermatomal hypesthesia and nominal or absent radicular pain typifies this unusual condition. Patients that have undergone treatment (both surgical and nonsurgical) have had no further progression or a decrease in the muscle hypertrophy.
In conclusion, recognizing the variability in muscle response to denervation is key to optimizing treatment in these patients.