Adult spinal muscular atrophy: problems of early diagnosis

Background. Spinal muscular atrophy (SMA) associated with chromosome 5q is an autosomal recessive neuromuscular disease caused by a mutation in the SMN1 gene. Adult forms of SMA are relatively rarer and associated with significant diagnostic difficulties and pronounced delay in diagnosis. The available pathogenetic therapy for SMA has the greatest effect with an earlier start of treatment, so timely diagnosis of the disease significantly improves the overall prognosis.
Aim. To evaluate the features of diagnosis of the adult SMA and summarize the first experience of such diagnosis in Russian patients.
Materials and methods. We analyzed the archived medical records of 50 adult patients with SMA consulted at the Research Center of Neurology (Moscow).
Results. The data of patients with SMA type 2 (n = 26), SMA type 3 (n = 21), SMA type 4 (n = 3) were analyzed. The delay time for diagnosis in SMA type 2 is 35 (0–270) months, with SMA types 3 and 4 – 108 (0–408) months. The diagnosis of SMA was the first diagnosis in SMA type 2 in 69 % of cases, in SMA types 3 and 4 in 29 % of cases. The most common first diagnosis in patients with SMA is myopathy, accounting for 52 % of all misdiagnosed cases. A small percentage of the use of needle electromyography in the diagnostic process was noted (1/3 of cases); in cases of its use, this did not accelerate the correct diagnosis. Creatine phosphokinase activity is often elevated in patients with SMA types 3 and 4 compared with SMA type 2 (p <0.05).
Conclusions. To reduce the delay in the correct diagnosis of SMA and earlier initiation of pathogenetic therapy, it is necessary to increase the awareness of specialists about the features of diagnosis the disease and focus on alternative erroneous diagnoses, among which adult patients with SMA may “hide”. The key to confirming the diagnosis is DNA testing.