Neuromuscular conditions are complex and varied in nature and can present as a primary condition or in association with other problems.
Their symptoms can also be quite varied and difficult to elicit, but as they progress it can start with weaknesses in in big muscle groups initially before smaller ones such as your respiratory (breathing) muscles.
Neuromuscular conditions are usually diagnosed through a mixture of clinical history/examination and investigations such as nerve conduction tests, muscle biopsies and imaging.
If you are concerned about a NMD, it maybe worth seeking help from a neurologist who specialises in this area of medicine.
Hope this helps.
BW
Dr Dinesh