Transient leg nodules.

A 14-year-old male presented to a pediatric dermatology clinic for painful skin-colored leg nodules (Fig 1). For the past 7 months, these nodules would transiently appear and disappear on his left lower leg while walking far distances or uphill. In the clinic, standing or bearing weight on the leg elicited the appearance of the nodules while plantar flexion of the foot and cessation of weight bearing caused the nodules to disappear (Video 1, available on www.jaad.org). The patient had previously seen other medical providers and underwent static leg ultrasound and magnetic resonance imaging (MRI) studies which revealed no abnormalities.

Fig 1

Question 1: What is the most likely diagnosis?

Lipoma

Vascular malformation

Epidermal inclusion cyst

Dermatofibroma

Tibialis anterior muscle herniation

Answer:

Lipoma — Incorrect. Lipomas are slow-growing benign fat tissue tumors that can present as flesh-colored nodules. They would not disappear upon movement and are not typically painful.

Vascular malformation — Incorrect. Vascular malformations are due to abnormal development of capillaries, veins, arteries, or lymphatics and, while not always noticed at birth, typically present in the first decade of life and would be visualized by ultrasound or MRI.

Epidermal inclusion cyst — Incorrect. Epidermal inclusion cysts present as a subcutaneous nodule that may fluctuate in size over time. However, movement would not cause them to transiently appear and disappear.

Dermatofibroma — Incorrect. Dermatofibromas are common fibrous nodules that dimple upon pinching of surrounding skin. They would not completely reduce in size and are usually less than 1 cm.

Tibialis anterior muscle herniation — Correct. The clinical history and physical examination findings showing reproducibility of the transient nodules are consistent with tibialis anterior muscle herniation. This is a rare, benign condition seen in younger adults or adolescents where the muscle herniates through fascial defects causing subcutaneous lower extremity nodules that change with limb movement.

Question 2: What is necessary for diagnosis?

MRI

Tissue biopsy

Wide excision

Computed tomography

None of the above

Answer:

MRI — Incorrect. MRI, which is much more expensive than ultrasound, may miss the initial diagnosis and may not even provide additional information as a subsequent test.,

Tissue biopsy — Incorrect. Tissue biopsy would be invasive and unnecessary.

Wide excision — Incorrect. Wide excision would be invasive and unnecessary.

Computed tomography — Incorrect. Computed tomography, which is much more expensive than ultrasound, has poor differentiation between fascia and muscle, which would limit its utility in diagnosing anterior tibialis muscle herniation.

None of the above — Correct. Diagnosis of anterior tibialis herniation relies primarily on clinical suspicion and physical examination findings. If needed, dynamic ultrasound imaging is sensitive and can detect fascial defects in anterior tibialis muscle herniation.1, 2, 3

Question 3: How do you treat this condition?

Compression stockings

Physical therapy

Longitudinal fasciotomy

Closure of fascial defect

A-C.

Answer:

Compression stockings — Incorrect. While compression stockings may be used in mild cases, severe cases may require surgery.

Physical therapy — Incorrect. While physical therapy may be used in mild cases, severe cases may require surgery.

Longitudinal fasciotomy — Incorrect. While severe cases with nerve entrapment may require muscle fasciotomy to release the entrapped nerve,, less symptomatic herniations would not require this invasive procedure.

Closure of fascial defect — Incorrect. While this has been used to treat muscle herniation, there is risk of compartment syndrome and thus fascial defect closure is not recommended.

A-C — Correct. Symptomatic treatment of anterior tibialis muscle herniation can include physical therapy and compression garments, while more definitive treatment, longitudinal fasciotomy, is reserved for severe cases which can involve nerve entrapment.,,

Conflicts of interest

None disclosed.