Introduction
Progressive muscular atrophy (PMA) is a very rare disease and one of the neuromuscular diseases with lower motor neuron(LMN) symptoms. LMN degeneration occurs, resulting in muscle weakness, atrophy, and fasciculation.
Hypokalemic periodic paralysis (HypoPP) is an autosomal dominantly inherited channelopathy, which is temporarily paralyzed with a decrease in potassium level in the blood. The life expectancy is normal, but in some cases, proximal myopathy may occur at a late age. However, PMA in HypoPP patients is not well known. We report a case in which a patient with a history of HypoPP is identified as PMA.
Case report
A 64 - year - old patient visited the outpatient clinic due to weakness of the ankle. The patient had a history of periodic paralysis that improved after potassium injection in his childhood. In MMT, the first left toe and ankle dorsiflexor muscle was grade 1, and the patient complains of tingling pain in the left whole lower extremity. In both knee and ankle, DTR was normotonous and UMN sign was not observed. Atrophy was detected in the left vastus medialis, tibialis anterior, and extensor digitorum brevis muscles. In the electromyography test, Left lower limb CMAP amplitude was abnormal compared to the right. H-reflex was normal on both side. The reinnervation pattern was confirmed in the left lower limb muscles(Table 1). Lt. Lumbosacral plexopathy with sciatic neuropathy was diagnosed and sciatic neuropathy was considered to be improving. Two years later, the patient returned to the outpatient clinic due to weakness on the contralateral lower extremity. In MMT, bilateral ankle and 1st toe dorsiflexor muscle strength were identified as grade 1. Muscle strength of bilateral toe, left plantarflexor, and left knee and hip were grade 2. Other leg strengths were identified as grade 3. The bilateral DTR was decreased in both sides. Both lower limb CMAP amplitudes were abnormal. The denervation pattern and reinnervation pattern were observed in needle EMG performed in both lower extremities muscles(Table 2). The patient was admitted with suspicion of motor neuron disease, and there were no lesions that caused weakness in brain and spine MRI(Figure 1). Genetic testing excluded other genetic diseases. Tongue fasciculation was confirmed and UMN sign did not appear. The patient was diagnosed with PMA.
Discussion
Myopathy after HypoPP is relatively well known, and because of the specific findings in electromyography, rapid diagnosis is possible, but the relationship between PMA and HypoPP is not well known. It is difficult to diagnose PMA patients whose initial symptoms is foot drop because they show similar findings to polyradiculopathy in electromyography study. Therefore, if a patient with a history of HypoPP develops weakness after middle age, serial electromyography study must be performed and careful observation should be made to see if a new abnormality has occurred in the area that was initially normal. |
