Pathophysiology of Pes Cavus in Charcot-Marie-Tooth Disease
Pes cavus in Charcot-Marie-Tooth disease results primarily from selective denervation and atrophy of the intrinsic foot muscles, particularly the lumbricals, rather than from imbalance of extrinsic lower-leg muscles. 1
Primary Mechanism: Intrinsic Muscle Denervation
The fundamental pathophysiologic process involves progressive denervation of the small muscles within the foot itself:
- Intrinsic foot muscle atrophy, especially the lumbricals, is the initial and primary mechanism causing reduced ankle flexibility and forefoot cavus deformity 1
- The insidious atrophy of intrinsic foot musculature progresses to create a fixed soft tissue and eventually bony cavus deformity 2
- This selective denervation pattern is an early and age-dependent manifestation of CMT1A duplication, the most common subtype 1
Secondary Mechanism: Extrinsic Muscle Imbalance
While intrinsic muscle denervation initiates the deformity, extrinsic muscle imbalance contributes to progression:
- Relative imbalance develops between the peroneus longus and tibialis anterior muscles 3
- Additional imbalance occurs between the tibialis posterior and peroneus brevis muscles 3
- Objective measurements demonstrate significantly higher strength ratios of inversion-to-eversion and plantarflexion-to-dorsiflexion in CMT patients with pes cavus compared to normal controls 4
- All foot and ankle muscle groups are significantly weaker in CMT patients compared to healthy individuals 4
Clinical Implications
The deformity follows a predictable progression from flexible to fixed:
- Pes cavus appears as a cardinal and nearly universal sign, present in all affected individuals in documented kinships 2
- The deformity begins as flexible but becomes progressively rigid over time 5, 3
- Early intervention targeting flexible deformities can restore normal foot posture and potentially delay more extensive bony procedures 3
Important Clinical Caveat
Do not confuse CMT-related pes cavus with Charcot neuro-osteoarthropathy (Charcot foot), which is an entirely different condition occurring in patients with peripheral neuropathy and diabetes, involving inflammatory bone and joint destruction 6, 7. While both conditions involve neuropathy, CMT causes pes cavus through gradual muscle denervation, whereas Charcot foot causes acute inflammatory bone destruction.