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English: Inherited calf hypertrophy since early childhood due to an undiagnosed myopathy in a transmale (female-to-male) individual. Other female and male family members of older and younger generations also have childhood-onset or adolescence-onset hypertrophy of calf muscles without being athletes or engaging in activity that would normally explain the hypertrophy.

For the individual in the image, combined T1-weighted MRI of the legs (lower legs MRI performed at age 32, upper legs MRI performed at age 34) showed no fatty atrophy of muscles (no fatty infiltration or pseudohypertrophy), overall muscle bulk symmetric, no muscle edema, thigh and calf musculature bilaterally unremarkable, neurovascular bundles unremarkable, sciatic nerve bilaterally unremarkable, joints (sacroiliac, pubic symphysis and hip) bilaterally unremarkable, lower lumbar spine and facet joints unremarkable, no findings to suggest myositis.

Arterial studies in legs were normal (negative for chronic venous insufficiency and claudication), MRI also negative for popliteal artery entrapment syndrome. Oxygen saturation during exercise stress test was normal (no ischemia) and echocardiogram was normal. 24-hour HOLTER monitor showed 53% sinus tachycardia and 4% sinus bradycardia.

At age 35, exercise stress test (treadmill with increasing speed and incline/grade) showed an inappropriate rapid heart rate response to exercise, elevated blood pressure, and heavy, rapid breathing. Heart rate, blood pressure, and breathing returned to normal with rest. Exercise stress test stopped due to increasing muscle fatigue, cramping sensation, and pain in the legs that became intolerable. Reached walking speed of 4.2 MPH at a 16% grade with a maximum heart rate of 187 BPM (101% of the maximal, age-predicted heart rate) and maximum blood pressure of 158/78 mmHg.

When walking without an incline (on level ground) signs and symptoms of exercise intolerance improve after approximately 10 minutes, suggestive of the second wind phenomenon of a muscle glycogenosis. When in ketosis, symptoms of exercise intolerance improve in approximately 3 minutes. (Ketones convert to acetyl CoA much faster than fatty acids.)

Exercise intolerance for high-intensity aerobic activity (such as brisk walking/running or stirring a pot fast) and anaerobic activity (walking uphill or opening a stuck jam jar) both of which rely predominantly on muscle glycogen.

Able to repeatedly do short bursts of anaerobic and high-intensity aerobic activity of a few seconds (within the time limit of the phosphagen system) provided that there is approximately 30 seconds rest between each burst (the time that it takes to replenish ATP-PCr by at least 80%), which again is suggestive of a muscle glycogenosis.

Blood tests normal except for uric acid. Uric acid increases significantly after exercise (walking for one hour), and decreases significantly with continued rest (suggestive of exercise-induced myogenic hyperuricemia, which is also seen in muscle glycogenoses). At rest, mild hyperuricemia (7.2 - 8.1 mg/dL). After exercise, hyperuricemia (9.4 - 11.0 mg/dL). Vegetarian diet, no excessive intake of purines, alcohol, fructose or other carbohydrates to explain the hyperuricemia. Since childhood, occasional joint pain experienced in the evening that resolves by morning. This joint pain occurs predominantly in the leg joints (bilaterally), but has also occurred in the shoulder and elbow joints synchronous with muscle aches in the corresponding arm.

No diabetes (random and fasting blood glucose normal), no abnormal thyroid (TSH normal), electrolyte panel (Na, K, Cl, CO2, Anion Gap) normal, creatinine normal, CK normal. Nerve conduction studies normal, EMG mix of normal and myopathic features (small amplitude, polyphasic, short duration units) recruitment was normal however.

No fixed muscle weakness, nor any muscle atrophy. Bilateral mild plantarflexion contracture and pronating ankles (flexible flatfeet). Other family members that likewise have a pseudoathletic appearance of hypertrophic calf muscles don't have contractures.

Whole exome sequencing panel for neuromuscular diseases (including muscle GSDs 0-15) negative for any known pathological variants. VUS (variants of unknown significance) in genes COL12A1, DMD, CCDC78, and FKTN.

Not likely to be Bethlem myopathy 2 (gene COL12A1) on account of the gross lack of corresponding signs and symptoms, and lack of contractures in other affected family members.

Not likely to be a symptomatic carrier of Duchenne or Becker muscular dystrophy (gene DMD) due to symmetrical muscle bulk and the older generation male family member (chromosomes XY) not showing typical symptoms that would be expected of Duchenne or Becker muscular dystrophy.

Not likely to be centronuclear myopathy 4 (gene CCDC78) due to gross lack of corresponding signs and symptoms.

Not likely to be Limb-girdle muscular dystrophy types A4, B4, or C4 (gene FKTN) due to gross lack of corresponding signs and symptoms.