Weakness of the limb girdle type with finger tremor and elevated creatine kinase

Aims: The workup of muscle weakness of the limb girdle type may be confusing. The purpose of this case report is to show how a few clinical and electromyographic results may help to find the correct diagnosis.

Methods: The clinical, electromyography (EMG), and laboratory data of a 17-year-old boy are presented.

Results: No neuromuscular diseases were found in his family. The motor development during the first years was normal. The boy had started to walk at the age of 13 months. From the beginning of school age, a stackness during sporting activity was observed, and from the age of 8 years, he would fatigue during hiking after a few minutes. From the age of 13 years, he was unable to stand up by himself during snowboarding, and a few months later, he could no more stand up from the squat.

A neurological examination revealed a proximal muscle weakness (legs > arms) with difficulty to stand up from a sitting position and to lift his arms, an irregular tremor of the fingers, no fasciculations of the tongue, and a moderate hypertrophy of the calves.

The EMG of the M. vastus lateralis showed single oscillations after maximal voluntary activity, motor unit potentials with increased duration, and amplitude but no spontaneous activity. The NCV was normal and the creatine kinase (CK) in the blood was 1880 U/L (normal < 270U/L). In the muscle biopsy, an increased number of atrophic fibers was detectable. Deletion of the survival motor neuron protein (SMN1)-specific exons 7 and 8 as well as four copies of SMN2 exons on chr. 5q13.2 was detected.

Conclusion: Proximally pronounced muscle weakness combined with elevated CK values are the main elements of limb-girdle muscular dystrophy (LGMD). However, the finger tremor and the neurogenic EMG are, despite elevated CK values, diagnostic elements, which exclude an LGMD and support a neurogenic cause of the weakness. Thereafter, a spinal muscular atrophy type 3 (SMA3) was genetically confirmed. Elevated CK values are described in male SMA3 patients with calf hypertrophy. To avoid unnecessary investigations, an EMG should be performed as the first test in the workup of patients with progressive muscle weakness of the limb-girdle type.