Stress-Induced Ketoacidosis in Spinal Muscular Atrophy: An Under-Recognized Complication

Metabolic Dysfunction in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder leading to paralysis, muscle atrophy, and death. Significant advances in antisense oligonucleotide treatment and gene therapy have made it possible for SMA patients to benefit from improvements in many aspects of the once devastating natural history of the disease. How the depletion of survival motor neuron (SMN) protein, the product of the gene implicated in the disease, leads to the consequent pathogenic changes remains unresolved. Over the past few years, evidence toward a potential contribution of gastrointestinal, metabolic, and endocrine defects to disease phenotype has surfaced. These findings ranged from disrupted body composition, gastrointestinal tract, fatty acid, glucose, amino acid, and hormonal regulation. Together, these changes could have a meaningful clinical impact on disease traits. However, it is currently unclear whether these findings are secondary to widespread denervation or unique to the SMA phenotype. This review provides an in-depth account of metabolism-related research available to date, with a discussion of unique features compared to other motor neuron and related disorders.

Metabolic and Nutritional Issues Associated with Spinal Muscular Atrophy

Spinal muscular atrophy (SMA), the main genetic cause of infant death, is a neurodegenerative disease characterized by the selective loss of motor neurons in the anterior horn of the spinal cord, accompanied by muscle wasting. Pathomechanically, SMA is caused by low levels of the survival motor neuron protein (SMN) resulting from the loss of the SMN1 gene. However, emerging research extends the pathogenic effect of SMN deficiency beyond motor neurons. A variety of metabolic abnormalities, especially altered fatty acid metabolism and impaired glucose tolerance, has been described in isolated cases of SMA; therefore, the impact of SMN deficiency in metabolic abnormalities has been speculated. Although the life expectancy of these patients has increased due to novel disease-modifying therapies and standardization of care, understanding of the involvement of metabolism and nutrition in SMA is still limited. Optimal nutrition support and metabolic monitoring are essential for patients with SMA, and a comprehensive nutritional assessment can guide personalized nutritional therapy for this vulnerable population. It has recently been suggested that metabolomics studies before and after the onset of SMA in patients can provide valuable information about the direct or indirect effects of SMN deficiency on metabolic abnormalities. Furthermore, identifying and quantifying the specific metabolites in SMA patients may serve as an authentic biomarker or therapeutic target for SMA. Here, we review the main epidemiological and mechanistic findings that link metabolic changes to SMA and further discuss the principles of metabolomics as a novel approach to seek biomarkers and therapeutic insights in SMA.

[Severe ketoacidosis induced by short-term starvation in a patient with spinal muscular atrophy]

We report a case of a 29-year-old woman with spinal muscular atrophy (SMA) type II who developed severe ketoacidosis after short-term starvation. She was hospitalized with lower respiratory tract infection. Although her symptoms improved after administration of intravenous antibiotic agents, her food intake gradually decreased. On the 7th day of hospitalization, she experienced abdominal pain followed by vomiting, after which she was unable to eat. Approximately 12 h later, she suffered from shock, accompanied with disturbance of consciousness, and she was admitted to the intensive care unit. She was diagnosed with ketoacidosis based on arterial blood gas analyses and urine test results. On receiving continuous infusion of glucose and insulin, her ketoacidosis was rapidly resolved and her symptoms completely recovered by the next day. To prevent the recurrence of ketoacidosis, we provided a diet plan based on indirect calorimetry results. However, ketoacidosis recurred twice, at 12 months and 16 months after discharge, both within 24 h of the onset of the fasting state. In addition to insufficient glycogen storage because of chronic malnutrition, poor gluconeogenesis or poor ketone body consumption due to skeletal muscle atrophy was believed to increase the risk of acute-onset, severe ketoacidosis after short-term starvation. Clinicians must note that patients with SMA are prone to ketoacidosis and that they must be promptly treated.

Euglycemic Ketoacidosis in Spinal Muscular Atrophy

Euglycemic ketoacidosis is defined by the triad of high anion gap acidosis, increased plasma ketones, and the absence of hyperglycemia. Apart from diabetes mellitus, the disorder may occur in prolonged fasting, excessive alcohol consumption, pregnancy, and inborn errors of metabolism. Here, we highlight the diagnosis of euglycemic ketoacidosis in a pediatric nondiabetic patient with spinal muscular atrophy (SMA) type 1 (Werdnig–Hoffmann disease), who, subsequently to her postoperative admission to the intensive care unit following a spinal surgery, developed high anion gap metabolic acidosis. We discuss the pathophysiology of acid-base disorders in SMA, along with the glucose and fatty acids metabolism, the necessary knowledge for medical practitioners.

Severe ketoacidosis in a patient with spinal muscular atrophy

Spinal muscular atrophy (SMA) is a genetic neuromuscular disease characterized by progressive muscle weakness and atrophy. We report a case of a 36-year-old man with SMA type 3 who presented to our emergency department with epigastric pain and vomiting. He was found to have severe ketoacidosis on laboratory evaluation. The patient's symptoms and ketoacidosis resolved after dextrose infusion and a relatively small amount of sodium bicarbonate infusion. Given the severity of the ketosis that seemed inconsistent with moderate starvation alone, we postulate that there must have been other contributing factors besides moderate starvation that might explain the severity of acidosis in this particular patient. These factors include low muscle mass, disturbed fatty acid metabolism, hormonal imbalances and defective glucose metabolism. Ketoacidosis is an under-recognized entity in patients with neuromuscular diseases and requires a high index of suspicion for prompt diagnosis and management.