the spectrum of clinical and electrophysiological features in hereditary neuropathy with liability to pressure palsies ( hnpp ) is broad and may range from clinically asymptomatic or subclinical to recurrent palsies and in some advanced cases , generalized neuropathies . hnpp has specific clinical and electrophysiological characteristics , but there are few studies describing their characteristics in a series of brazilian patients to date . the aim of our study was to analyze a series of hnpp patients to contribute to better characterization of the disease in southern brazil . a retrospective analysis of 3828 patients who underwent electrophysiological analysis from 2004 to 2015 revealed 10 patients with a diagnosis of hnpp , according to three of the following obligatory criteria : typical clinical features , familial history , abnormal electrophysiological analysis and absence of other causes of neuropathy on follow - up at least one year after the diagnosis . relevant data included age , age at onset ( first episode of acute nerve palsy ) , gender , clinical manifestations , and other affected relatives . characteristics of acute nerve palsy episodes and concomitance of generalized symmetric neuropathy were recorded . cerebrospinal fluid ( csf ) protein level was classified as normal ( < 45 mg / dl ) or increased ( 45 mg / dl ) . motor and sensory nerve conduction studies ( ncs ) were performed bilaterally using neuropack 2 or m1 ( nihon kohden ) machines according to routine protocols . we considered all examined segments in the evaluation of conduction block ( cb ) , defined as a reduction greater than 50% in proximal compared with distal potential amplitude associated with temporal dispersion . the pmp22 gene was subjected to polymerase chain reaction - restriction fragment length polymorphism ( pcr / rflp ) analysis , consisting of pcr , which produced a 3,6 kbp fragment , followed by restriction endonuclease digestion with ecori , according to standard procedures . wild - type dna produced fragments ( 3.2 and 0.4 kbp ) , whereas dna from patients heterozygous for the mutation presented three fragments ( 3.6 , 3.2 and 0.4 kpb ) because , in the presence of the putative mutation ( deletion of the 1.5-mb region in the pmp22 gene ) the 3.6-kbp fragment is not cleaved into two fragments . a diagnosis was made during the first palsy episode in two cases and in the remaining three cases , a diagnosis was obtained before the palsy episode considering electrophysiological analysis and the presence of affected family members . table 1 shows focal sites at first nerve palsy and recurrent episodes ; three cases did not report any acute nerve palsy episodes . ncs showed focal neuropathy ( abnormal conduction velocities limited to entrapment or compression sites ) in all patients and concomitant generalized symmetrical neuropathy in eight patients ( table 1 ) . emg revealed denervation findings in six patients and dystonic findings ( concomitant activity of agonist and antagonist muscles during writing task ) in case 5 ( table 1 ) . csf protein level was mildly increased ( 57 mg / dl ) in one patient ( table 1 ) . molecular analysis of the pmp22 gene detected deletion of the 1.5-mb fragment in all patients . findings in our patients are , in general , similar to those previously described . although in our cases , the clinical and electrophysiological phenotype was not homogeneous within the same family . some patients presented with an atypical spectrum of findings , which can occur in up to 56% of hnpp patients . in our patients , the peroneal and ulnar nerves were the most vulnerable , but they presented a higher frequency of radial nerve palsy than previously reported , including the site of first nerve palsy episode , as well as uncommon suprascapular nerve palsy ( case 10 ) . also , one patient ( case 1 ) was previously reported due to recurrent episodes of swallowing dysfunction and three patients presented carpal tunnel syndrome as the main manifestation , which helps to confirm that cranial nerve palsy and chronic mononeuropathies are relevant in hnpp . in addition , one patient ( case 5 ) presented clinical features of writer s cramp , which has persisted since his ulnar nerve palsy . writer s cramp caused by hnpp was reported only once as a possible result of persistent compensation after nerve palsy . we speculated that a similar mechanism , and maybe an aberrant reinervation , could be occurring in our patient , which allowed us to include hnpp as one more etiology causing writer s cramp . ncs are usually characterized by a generalized demyelinating neuropathy with conduction abnormalities preferentially localized at common entrapment sites , similar to what we observed in our cases . electrophysiological analysis detected three patients in affected families before acute nerve palsy had become apparent . cb seems to have a higher frequency when nerve palsy occurs in childhood , but this may be because ncs were performed closer to the nerve palsy episode . indeed , we did not find studies comparing ncs features at acute episode and after long - term outcome . the difference between age at onset and at diagnosis in our patients suggests that cb is not often observed after long - term outcome of a nerve palsy episode ; however , this feature is not restricted to hnpp because it can occur in immune - mediated neuropathies . high csf protein level and tomacula in the nerve biopsy may be useful in differential diagnosis when no affected family member is reported at first . however , these finding are not a specific marker for hnpp and they should be avoid if ncs can be followed by genetic analysis . the typical 1.5-mb deletion in the pmp22 gene is usually found in approximately 85 to 90% of patients with clinical evidence of hnpp . although most analyses have been limited to populations from north america and europe , this mutation has been reported in brazil . our study , despite being a small series , contributes to the idea that this mutation is also frequent in brazilian patients .
the spectrum of clinical and electrophysiological features in hereditary neuropathy with liability to pressure palsies ( hnpp ) is broad . 
 we analyze a series of brazilian patients with hnpp . 
 correlations between clinical manifestations , laboratory features , electrophysiological analyze , histological and molecular findings were done . in five cases , more than one episode occurred before diagnosis . 
 median nerve in the carpal tunnel at the wrist , ulnar nerve in its groove at the elbow , fibular nerve in the head of the fibula at the knee , radial nerve in its groove of the humerus and suprascapular nerve in its notch at the supraspinous fossa were found as focal neuropathies . 
 one patient presented with persistent writer s cramp after ulnar nerve palsy . 
 nerve conduction studies showed focal neuropathy in all patients and concomitant generalized symmetrical neuropathy in eight patients . 
 molecular analysis of the pmp22 gene detected deletion of the 1.5-mb fragment in all patients .