Spinal Muscular Atrophy (SMA)

 SMA is a genetic neuromuscular disease characterized by progressive degeneration of lower motor neurons (alpha motor neurons in the anterior horn). There is amyotrophy without sensorial or pyramidal tract signs.

It is a genetically heterogeneous disease; SMA is inherited as autosomal recessive (most common), autosomal dominant and X-linked recessive forms. SMA is the second most common autosomal recessive disorder. Its incidence is 1-2 per 10,000 live births. SMA is the most common neuromuscular disease in childhood after Duchenne Muscular Dystrophy (DMD).

SMA presents with weakness, atrophy or fasciculation in the muscles. If the child has hypotonia with weakness, a great deal of SMA should be suspected. The weakness is generally symmetrical and commonly the proximal muscles such as the shoulder girdle and hip girdle are involved. Leg weakness is more than in the arms. The sensation is normal and the reflexes are reduced or lost. SMA usually affects the shoulder and hip girdle and proximal muscles. Creatine Kinase (CK) is normal in acute conditions, and high in chronic conditions. SMA is usually diagnosed through a blood test to check for the presence of the SMN1 gene (genetic testing). Spinal muscular atrophy is due to a genetic defect in the SMN1 gene.

SMA Types

SMA Type 1: which is also known as Werdnig Hoffmann's Disease is the most severe form of SMA with symptoms usually beginning between 0 and 6 months. Babies are unable to sit without support. Babies diagnosed with SMA type 1 do not generally live past two years of age. Babies can not hold their head because of weakness and hypotonia. Their voice is weak, they has difficulty swallowing and breathing.

SMA Type 2: symptoms usually begin between the ages of 7 and 18 months. Children are unable to stand without support and may be described as ‘sitters’. Babies with SMA type 2 can never walk. The child lives more than 2 years. Movements are delayed, they gain less weight, there may be a slight cough, tremors in the hands. Contractures and scoliosis may develop in these children.

SMA Type 3: It is mild form of the SMA. It is also called Kugelberg Welander Disease. It occurs after 18 months of age. Children can stand and walk, though this will become more difficult with age and they will need more support over time. There may be cramps in the muscles.

SMA Type 4: It is slight form of SMA. Symptoms begin in adulthood.

Treatment

Patients should be carefully monitored for breathing, swallowing and nutritional problems. In December 2016, the US Food and Drug Administration (FDA) approved Nusinersen (Spinraza), the first drug to treat SMA. Nusinersen can slow, stop, and even reject SMA symptoms. Patients who use medication should continue rehabilitation without interruption in order to obtain sufficient results from the drug.

Rehabilitation

Rehabilitation is organized according to the stages of SMA and the needs of the patient. The rehabilitation process starts after the birth and continues at every stage of the disease. It is tried to facilitate the life of the patient with auxiliary devices. SMA rehabilitation is performed similar to ALS and myopathy rehabilitation. Although the basic principles are the same, patients can be grouped as  non-sitters, sitters and walkers.

Non-sitters: The non-sitters include the group of children who currently are not able to sit independently. The appropriate device is selected to ensure that the child sits comfortably. The nutrition is regulated ans supported. Swallowing and speech problems are treated speech therapist. Range of motion exercises are started to prevent contracture. Basic toys, controlled support systems and activations are selected to improve child’s skills.

Sitters: The seated adult or child is assessed by the Hammersmith or Modified Hammersmith Functional Motor Scale for SMA, the Gross Motor Function Scale (GMFM) and the Motor Function Scale for neuromuscular diseases. Contractures are determined by goniometer, muscle strength by manual muscle test. Scoliosis and hip dislocation can be detected radiographically. The wheelchair is prescribed so that the patient is comfortable and gains optimal independence. The home and the environment are arranged in such a way that the patient feels safe and can do his work independently. Posture training and range of motion exercises are planned to maintain flexibility and prevent contractures. If a child develops contractures, stretching exercises are started. Serial casting helps correct joint alignment. Ankle-Foot-Orthosis (AFO) may delay achilles contracture. Standing should be supported. Standing prevents the contractures and deformities, as well as it can help maintain the balance and walking. Knee ankle foot orthoses (KAFO) and reciprocal gait orthosis (RGO) are used to assist in standing and walking. Aerobic exercise is recommended according to the patient's condition. Sports like aquatic exercises can be recommended.

Walkers: Bone mineral density is measured by DEXA, and osteoporosis medication is started. Patients mobilization is provided by a wheelchair. The patient is encouraged to walk with supportive orthoses and assistive walking devices. Muscle strength and endurance exercises are organized. Aerobic exercises such as swimming, hydrotherapy, horse riding can be used in a controlled manner. To prevent contracture development, range of motion exercises are performed regularly. If scoliosis and contracture develops, breys and devices are applied.

Surgery:

Surgical interventions are performed presence of contractures, hip dislocations and scoliosis. Scoliosis surgery gives good results in patients over 2-year old with adequate lung function.

SELECTED RESOURCES

-          Fırıncıoğulları M, Yavuz B , Koç F. Ön Boynuz Tutulumuyla Giden Hastalıklar (Anterior Horn Cell Diseases). Arşiv Kaynak Tarama Dergisi .(Archives Medical Review Journal) 2016; 25(4):269-303

-          Tiryaki E, Horak AH. ALS and other motor neuron diseases. Continuum (Minneap Minn) 2014;20:1185–1207

-          Sena Aslan E, Erbaş O. Motor neuron diseases: Amyotrophic lateral sclerosis and spinal muscular atrophy. D J Tx Sci 2019;4(1-2):46-51.