Layer of skin involved
The skin weighs an average of 4 kg (8.8 lb), covers an area of 2 m2 (22 sq ft), and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are glabrous skin, the nonhairy skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type,  hairs in structures called pilosebaceous units have a hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands are from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues. Epidermis
The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers via diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95% of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface.
Patients that present with permanent weakness are normally not characterized as having PC. Electromyography may be used to distinguish between paramyotonia congenita and myotonia congenita., Clinicians may also attempt to provoke episodes or myotonia and weakness/paralysis in patients in order to determine whether the patient has PC, hyperkalemic periodic paralysis, or one of the potassium-aggravated myotonias. Genomic sequencing of the SCN4A gene is the definitive diagnostic determinant. Treatment
Some patients do not require treatment to manage the symptoms of paramyotonia congenita. Others require treatment for their muscle stiffness and often find mexiletine to be helpful. Others have found acetazolamide to be helpful as well. Avoidance of myotonia triggering events is also an effective method of myotonia prevention. Epidemiology
Paramyotonia congenita is considered an extremely rare disorder, though little epidemiological work has been done. Prevalence is generally higher in European-derived populations and lower among Asians. Epidemiological estimates have been provided for the German population. There, it was estimated that the prevalence of PC is between 1:350,000 (0.00028%) and 1:180,000 (0.00056%). However, the German population of patients with PC is not uniformly distributed across the country. Many individuals with PC herald from the Ravensberg area in North-West Germany, where a founder effect seems to be responsible for most cases. The prevalence here is estimated at 1:6000 or 0.017%. History
Originally thought to be separate from hyperkalemic periodic paralysis and the sodium channel myotonias, there is now considerable disagreement as to whether these disorders represent separate entities or overlapping phenotypes of a complex disorder spectrum.