Mitochondriopathy as a differential diagnosis of amyotrophic lateral sclerosis.

OBJECTIVES

To assess how often mitochondrial myopathy (MMP) mimics amyotrophic lateral sclerosis (ALS) and the phenotypic similarities and differences between these two disorders.

METHODS

Records of 123 MMP patients and 59 ALS patients, diagnosed during five years (1996-2000), were retrospectively evaluated.

RESULTS

Re-evaluation revealed that 8 patients, initially diagnosed as ALS had actually MMP (13.6%). Among the MMP patients, 6.5% were initially misdiagnosed as ALS. None of the MMP patients actually had ALS. Common features of ALS and MMP were weakness, wasting, upper motor neurone signs, bulbar abnormalities, and a neurogenic EMG. Features differentiating MMP from ALS were ptosis, sensory disturbances, multi-system involvement, slowly progressive disease course, abnormal lactate stress test, histological and biochemical abnormalities, and mtDNA analysis.

CONCLUSIONS

In a small number of cases MMP may clinically and electrophysiologically mimic ALS, particularly in the early stages of the disease. Patients with suspected ALS, but slow progression and multi-organ involvement, should undergo lactate stress testing and muscle biopsy. ALS should be diagnosed only if MMP has been excluded.