Are there different forms of nemaline myopathy (ie. acute vs chronic)?
There are six forms of nemaline myopathy which are classified by the time of onset and severity. Severe congenital starts at birth and is very severe. These patients have very severe muscle weakness and little to no movements. Death usually occurs early on, but there are case reports of patients who survive long-term.
Amish nemaline myopathy is so described because it is only seen within the Old Order Amish community. It is present at birth with low muscle tone, shortened muscles which lead to abnormal joints, and tremors. They progress with significant deterioration of the muscles and death occurs within 2 years due to inability to breathe.
Intermediate congenital nemaline myopathy is present shortly after birth and there are shortened muscles that lead to abnormal joints (contractures). Weakness may necessitate use of a wheelchair and breathing support by age 11.
Typical congenital nemaline myopathy has symptoms begin within the first year of life. Muscle weakness, low muscle tone, and trouble eating are the usual signs. Some patients may have difficulties with breathing but this is not true for all patients. The muscle weakness tends to progress slowly and many patients can live independent lives.
Childhood-onset nemaline myopathy shows signs and symptoms in childhood up to the 20s. There is a foot drop: difficulty lifting up the front part of the foot, which is often the first sign. Muscle weakness is slow in its progession and may eventually require a wheelchair for mobility.
Signs and symptoms of adult-onset nemaline myopathy usually do not start until 20-50 years of age. A dropped head or neck weakness or cardiomyopathy may be the first signs of the disorder. The quickness of the progression of muscle weakness is quite variable in this form.