The diagnosis of mild spinal muscular atrophy (SMA) phenotypes can be particularly challenging and could have important consequences in the era of disease-modifying drugs, according to a case report recently published in the Journal of Neurological Sciences.
Because the majority of existing guidelines focus on SMA diagnosis and management during childhood, literature regarding SMA diagnosis in adulthood remains scarce. Due to the development of new gene-based therapies capable of preserving motor function in adult patients, making a correct diagnosis during adulthood has become even more important.
The present case involved a 32-year-old woman with a history of muscle weakness and increased tiredness after climbing stairs. Further questioning revealed that she had trouble standing up as a child but never needed any walking assistance. Physical exam showed decreased muscle strength in the lower limbs, with absent deep tendon reflexes. Cranial nerve and sensory examinations were unremarkable.
Laboratory studies revealed elevated serum creatinine kinase levels, which, combined with magnetic resonance imaging findings of fatty transformation and muscle atrophy along with unremarkable nerve conduction studies, initially pointed toward a diagnosis of myopathy. However, the asymmetric atrophy pattern involving the iliopsoas and quadriceps femoris muscles raised the suspicion of SMA and prompted the authors to perform electromyography (EMG).
Read more about SMA differential diagnosis
EMG revealed chronic neurogenic changes and fasciculations, further suggesting SMA. Initial exome sequencing was negative, but SMN1 gene analysis confirmed the SMA diagnosis. Although the patient was eligible for gene-based medication, because of the mild presentation of the disease and plans for pregnancy, treatment was postponed.
The authors hypothesize that the combination of elevated creatinine kinase levels and muscle weakness could point many clinicians toward a myopathy diagnosis, making EMG a critical diagnostic tool in adult SMA diagnosis.
“It further emphasizes the need to consider SMA among the differential diagnoses in ambulatory adult patients with a limb-girdle pattern of weakness and elevated [creatinine kinase] activity levels, especially in view of possible therapeutic consequences in the era of gene-based therapies,” the authors concluded.
Krenn M, Jengojan S, Grisold W. Spinal muscular atrophy presenting with mild limb-girdle weakness in adulthood: diagnostic pitfalls in the era of disease-modifying therapies. J Neurol Sci. Published online July 25, 2022. doi:10.1016/j.jns.2022.120347