Medical Mystery of the Week

Because of the COVID19 pandemic, you are practicing telemedicine. You are shown the hand writing of a 35-year-old woman who was asked to write her name three times in succession (see below).
      What is your diagnosis, what test(s) do you recommend to confirm your suspicions, and what treatment, if any, do you recommend? 

DIAGNOSIS: Myotonia congenita (MC).  MC is a congenital neuromuscular channelopathy due to a loss of function mutation in CLCN1 - the gene that encodes the CIC-1 chloride channel. The lack of a sufficient number of chloride channels in muscle fiber membranes leads to a  prolonged contraction and delayed relaxation of skeletal muscles. Hence, persons with MC have muscle stiffness, muscle cramping (including writer's cramp, as in the presented case), muscle spasm (particularly of masseter muscles), and in some forms of the disorder, muscle weakness. Exposure to cold and inactivity typically worsen the condition. MC can be inherited as an autosomal dominant trait (Thomsen disease) or an autosomal recessive trait (Becker disease).
      MC treatment includes avoiding prolonged periods of inactivity and exposure to cold.          Severe cases may require an anticonvulsant such as dilantin or carbamazepine.
      MC is sometimes referred to as the fainting goat syndrome as it is responsible for the eponymous "fainting" seen goats with the disorder when presented with a sudden stimulus. MC is also seen in cows and horses.
      The differential diagnosis of MC includes: 1. Sodium channel (SCN4A) myotonias including  potassium-aggravated myotonia (AKA acetazolamine responsive myotonia), hyperkalemic periodic paralysis, and paramyotonia congenita; 2. A potassium channel (KCNJ2) disorder - the Andersen-Tawil syndrome; 3. Myotonic dystrophy; 4. Neuromyotonia (Isaacs syndrome); 5. Schwartz-Jampel syndrome; 5. Stiff person syndrome; and 6. Brody myopathy.