J Orthopaed Traumatol (2010) 11:195–201 weakness and wasting also involve the distal upper limb muscles. Foot deformity is a common feature. Additional features are represented by involvement of hands, vocal cord paralysis, diaphragm paralysis, and pyramidal tract signs [35]. In dHMN patients, electromyography evidences signs of chronic denervation, and motor NCV study shows an amplitude reduction of compound muscle action potentials or a moderate decrease in velocity. Sensory nerve con- ductions and amplitudes were normal [4, 36]. Sural nerve biopsy has rarely been performed in dHMN patients and usually showed normal ﬁndings [4]. Muscle biopsy shows neurogenic damage related to lower motor neuron degeneration [37]. dHMN has no speciﬁc treatment. Patients need neuro- logical follow-up to evaluate the disease’s clinical pro- gression and for referral to rehabilitation or orthopedic service for correct management of complications. Etiopathogenesis of pes cavus in HPN Pes cavus in HPN derives from plantar ﬂexion deformity of the ﬁrst metatarsal due to imbalance between the intrinsic muscles of the foot and the muscles of the leg. The exact physiopathological mechanisms responsible for pes cavus genesis in HPN is not entirely clariﬁed, even if two main hypotheses have been formulated [38]. The ﬁrst hypothesis assigns an important role in the pathogenesis of this skeletal deformity to overaction of the peronei in comparison with the antagonist tibialis anterior, secondary to the leg muscle’s amyotrophy pattern in the disease. In particular, it has been supposed that a weak per- oneus brevis is overpowered by a relatively stronger tibialis posterior, causing adduction of the forefoot and inversion of the hindfoot. In addition, a weak tibialis anterior is overpowered by a stronger peroneus longus, causing plantar- ﬂexion of the ﬁrst metatarsal and anterior pes cavus [12, 39– 41]. The intrinsic foot muscles develop contractures, while the long extensor to the toe muscles, recruited to assist in ankle dorsiﬂexion, causes claw toes deformity. The second hypothesis is that precocious and primary involvement of intrinsic foot muscles is responsible for the pathogenesis of pes cavus, because the deformity is observed in the early stages of the disease, also when there is not yet evidence of leg muscle weakness [42]. A mag- netic resonance imaging (MRI) study of amyotrophic leg and foot muscles performed in patients with CMT [43] reported precocious fatty inﬁltration of intrinsic foot mus- cles, also when leg muscles are still preserved. The authors deduced that the weakness of the lumbricals and the other intrinsic foot muscles, due to selective denervation, could cause the dorsiﬂexion of metatarsophalangeal joints, 199 initially responsible for the ﬂattening of the transverse arcus plantaris and the clawing of the toes. Dorsiﬂexion of metatarsophalangeal joints during gait could also deter- mine the wrapping around the metatarsal head of the plantar aponeurosis and the contraction of the short ﬂexors, with secondary shortening of the Achilles tendon and limitation of ankle dorsiﬂexion. A subsequent MRI muscle study in CMT patients also seems to conﬁrm a possible primary role of intrinsic foot muscle in pes cavus patho- genesis [44]. The sensitivity of MRI for detecting preco- cious denervation changes in early stages of HMN and CMT has been also recently conﬁrmed [45]. In conclusion, the foot deformity pes cavus, secondary to plantar ﬂexion deformity of the ﬁrst metatarsal, could be associated to several neurological disorders, including spinal cord and peripheral nerve pathologies, such us spi- no-cerebellar ataxia and hereditary peripheral neuropathies. In this article, we have reported the HPN in which pes cavus plays a key role as a ‘‘spy sign’’ [46, 47], as a pre- cocious manifestation of HPN. Accurate clinical evaluation in patients with pes cavus is therefore necessary to exclude or conﬁrm the presence of contemporary involvement of peripheral nerves [48, 49], especially in the early stage of Fig. 3 When pes cavus might reveal HPN: a proposed diagnostic algorithm. NCS nerve conduction studies, HPN hereditary peripheral neuropathies 123