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In this case report, a 23-year-old normal-functioning young man was repeatedly admitted to the hospital with mal-nutrition and pseudo-obstruction. External ophthalmoplegia, global muscular atrophy and demyelinating sensory-motor-autonomic neuropathy became evident. An MRI showed symmetrical white matter lesions and muscle biopsy atrophic muscle fibres. A TYMP mutation confirmed the diagnosis, and the patient had a rapidly fatal disease course. Mitochondrial neuro-gastro-intestinal encephalo-myopathy is rare and often overlooked. In less advanced disease, stem cell transplantation can correct thymidine phosphorylase deficiency.

Mitochondria produce cellular energy, which is of vital importance for cellular metabolism. The organelles contain their own genetic material (i.e. mitochondrial DNA (mtDNA)) with a matrilineal inheritance. Mutations in the mtDNA may cause mitochondrial disease affecting multiple organs leading to diabetes, hearing impairment, muscle fatigue, ptosis and stroke-like episodes in varying combinations and severity. The variable phenotypic presentations make it a challenge to recognize mitochondrial diseases and, consequently, the correct diagnosis is often delayed.

We report the case of a man who had an insidious onset of asymmetrical distal muscle weakness of the upper extremity at the age of 17. Objective findings were 1) muscular atrophy of calf and forearm flexor muscles and intrinsic hand muscles; 2) fasciculations; and 3) hand tremor. EMG and muscle biopsy showed neurogenic changes. MRI of the medulla and plasma creatine kinase were normal. Genetic testing for SMA-III was negative.

Diagnostic evaluation of muscle disease has gained considerably from the expanding development in molecular science in the last decade. This paper gives an overview of current diagnostic procedures in the evaluation of patients with muscle disease. The role of the clinical examination, genetic and serological tests, neurophysiological examination, muscle imaging, muscle histology and exercise tests for the diagnosis of muscle disease are discussed.